<?xml version="1.0" encoding="US-ASCII"?>
<!--
Copyright 2008, 2009 University Corporation for Atmospheric Research

This file is part of the UDUNITS-2 package.  See the file COPYRIGHT
in the top-level source-directory of the package for copying and
redistribution conditions.

Units not accepted for use with the SI.  NB: <name> and <symbol>
elements appear only within <aliases>.
-->
<unit-system>
    <!-- Synonyms for SI Units -->
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>s</def>
            <aliases> <name> <singular>sec</singular> </name> </aliases>
            <definition>unit of time, synonym for second</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>A</def>
            <aliases> <name> <singular>amp</singular> </name> </aliases>
            <definition>unit of electric current, synonym for ampere</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>K</def>
            <aliases>
                <symbol comment="DEGREE SIGN">&#xB0;K</symbol>        
                <name>
                    <singular>degree_kelvin</singular>
                    <plural>degrees_kelvin</plural>
                </name>
                <name>
                    <singular>degree_K</singular>
                    <plural>degrees_K</plural>
                </name>
                <name>
                    <singular>degreeK</singular>
                    <plural>degreesK</plural>
                </name>
                <name>
                    <singular>deg_K</singular>
                    <plural>degs_K</plural>
                </name>
                <name>
                    <singular>degK</singular>
                    <plural>degsK</plural>
                </name>
            </aliases>
            <definition>unit of temperature, synonym for kelvin</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>cd</def>
            <aliases> <name> <singular>candle</singular> </name> </aliases>
            <definition>unit of luminous intensity, synonym for candela</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>mole</def>
            <aliases> <name> <singular>einstein</singular> </name> </aliases>
            <definition>unit of chemical mass, synonym for mole</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>Hz</def>
            <aliases>
                <name> <singular>baud</singular> </name>
                <symbol>Bd</symbol>
                <symbol>bps</symbol>
            </aliases>
            <definition>unit of frequency, synonym for hertz</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>degree_Celsius</def>
            <aliases>
                <symbol comment="DEGREE CELSIUS">&#x2103;</symbol>       
                <name> <singular>celsius</singular> </name>
                <name>
                    <singular>degree_C</singular>
                    <plural>degrees_C</plural>
                </name>
                <name>
                    <singular>degreeC</singular>
                    <plural>degreesC</plural>
                </name>
                <name>
                    <singular>deg_C</singular>
                    <plural>degs_C</plural>
                </name>
                <name>
                    <singular>degC</singular>
                    <plural>degsC</plural>
                </name>
            </aliases>
            <definition>unit of temperature, synonym for 'K @ 273.15' (degree_Celsius)</definition>
        </unit>
        <unit>
            <comment>Synonym for SI unit</comment>
            <def>knot</def>
            <aliases>
                <symbol>kt</symbol>
                <symbol>kts</symbol>
            </aliases>
            <definition>unit of speed, synonym for nautical_mile/hour</definition>
        </unit>

    <!-- Constants -->
        <unit>
            <comment>Constant; value is +-30e15</comment>
            <def>6.02214179e23/mol</def>
            <aliases>
                <name><singular>avogadro_constant</singular></name>
                <noplural/>
            </aliases>
            <definition>number of constituent particles (usually atoms or molecules) per mole of a given substance</definition>
        </unit>
        <unit>
            <comment>Constant</comment>
            <def>0.01</def>
            <aliases>
                <name><singular>percent</singular></name>
                <noplural/>
                <symbol>%</symbol>
            </aliases>
            <definition>number of parts per hundred</definition>
        </unit>
        <unit>
            <comment>Constant</comment>
            <def>1e-6</def>
            <aliases>
                <symbol>ppm</symbol>
                <symbol>ppmv</symbol>
            </aliases>
            <definition>parts per million</definition>
        </unit>
        <unit>
            <comment>Constant</comment>
            <def>1e-9</def>
            <aliases>
                <symbol>ppb</symbol>
                <symbol>ppbv</symbol>
            </aliases>
            <definition>parts per billion</definition>
        </unit>
        <unit>
            <comment>Constant</comment>
            <def>1e-12</def>
            <aliases>
                <symbol>ppt</symbol>
                <symbol>pptv</symbol>
            </aliases>
            <definition>parts per trillion</definition>
        </unit>
        <unit>
            <comment>Constant</comment>
            <def>1e-15</def>
            <aliases>
                <symbol>ppq</symbol>
                <symbol>ppqv</symbol>
            </aliases>
            <definition>parts per quadrillion</definition>
        </unit>

    <!-- Plane Angle -->
        <unit>
            <def>0.9 arc_degree</def>
            <aliases> <name><singular>grade</singular></name> </aliases>
            <definition>1/100 of a right angle (90 degrees)</definition>
        </unit>
        <unit>
            <def>2 pi rad</def>
            <aliases>
                <name><singular>circle</singular></name>
                <name><singular>cycle</singular></name>
                <name><singular>turn</singular></name>
                <name><singular>revolution</singular></name>
                <name><singular>rotation</singular></name>
            </aliases>
            <definition>unit of angle in a plane signifying a full 360-degree circle</definition>
        </unit>
        <unit>
            <def>arc_degree</def>
            <aliases>
                <name>
                    <singular>degree_north</singular>
                    <plural>degrees_north</plural>
                </name>
                <name>
                    <singular>degree_N</singular>
                    <plural>degrees_N</plural>
                </name>
                <name>
                    <singular>degreeN</singular>
                    <plural>degreesN</plural>
                </name>
                <name>
                    <singular>degree_east</singular>
                    <plural>degrees_east</plural>
                </name>
                <name>
                    <singular>degree_E</singular>
                    <plural>degrees_E</plural>
                </name>
                <name>
                    <singular>degreeE</singular>
                    <plural>degreesE</plural>
                </name>
                <name>
                    <singular>degree_true</singular>
                    <plural>degrees_true</plural>
                </name>
                <name>
                    <singular>degree_T</singular>
                    <plural>degrees_T</plural>
                </name>
                <name>
                    <singular>degreeT</singular>
                    <plural>degreesT</plural>
                </name>
            </aliases>
            <definition>unit of angle on a sphere</definition>
        </unit>
        <unit>
            <def>-1 degree_east</def>
            <aliases>
                <name>
                    <singular>degree_west</singular>
                    <plural>degrees_west</plural>
                </name>
                <name>
                    <singular>degree_W</singular>
                    <plural>degrees_W</plural>
                </name>
                <name>
                    <singular>degreeW</singular>
                    <plural>degreesW</plural>
                </name>
            </aliases>
            <definition>unit of angle on a sphere (units for negative direction)</definition>
        </unit>

    <!-- Mass -->
        <unit>
            <def>2.916667e-2 kg</def>
            <aliases>
                <name> <singular>assay_ton</singular> </name>
            </aliases>
            <definition>reference unit of mass for a body of ore; roughly equal to 29167 milligrams</definition>
        </unit>
        <unit>
            <def>2.834952e-2 kg</def>
            <aliases>
                <name> <singular>avoirdupois_ounce</singular> </name>
            </aliases>
            <definition>unit of mass equal to 1/16 avoirdupois pound, commonly used in the United States (16 oz = 1 pound = 7000 grains)</definition>
        </unit>
        <unit>
            <def>4.5359237e-1 kg</def>
            <aliases>
                <name> <singular>avoirdupois_pound</singular> </name>
                <name> <singular>pound</singular> </name>
                <symbol>lb</symbol>
            </aliases>
            <definition>unit of mass in avoirdupois system of weights (a system commonly used in United States)</definition>
        </unit>
        <unit>
            <def>2e-4 kg</def>
            <aliases>
                <name> <singular>carat</singular> </name>
            </aliases>
            <definition>unit of mass equal to 0.2 gram (defined 1907)</definition>
        </unit>
        <unit>
            <def>6.479891e-5 kg</def>
            <aliases>
                <name> <singular>grain</singular> </name>
                <symbol>gr</symbol>
            </aliases>
            <definition>unit of mass equal to 1/7000 pound</definition>
        </unit>
        <unit>
            <def>5.080235e1 kg</def>
            <aliases>
                <name> <singular>long_hundredweight</singular> </name>
            </aliases>
            <definition>unit of mass; a British hundredweight, which is 8 stone * 14 pounds/stone</definition>
        </unit>
        <unit>
            <def>1.555174e-3 kg</def>
            <aliases>
                <name> <singular>pennyweight</singular> </name>
            </aliases>
            <definition>unit of mass; based on historical US troy weight system (is 1/20 troy ounce)</definition>
        </unit>
        <unit>
            <def>4.535924e1 kg</def>
            <aliases>
                <name> <singular>short_hundredweight</singular> </name>
            </aliases>
            <definition>unit of mass, a US hundredweight, which is 100 pounds</definition>
        </unit>
        <unit>
            <def>14.59390 kg</def>
            <aliases>
                <name> <singular>slug</singular> </name>
            </aliases>
            <definition>unit of mass associated with Imperial units; a mass that accelerates by 1 ft/s2 when a force of one pound-force (lbF) is exerted on it</definition>
        </unit>
        <unit>
            <def>3.110348e-2 kg</def>
            <aliases>
                <name> <singular>troy_ounce</singular> </name>
                <name> <singular>apothecary_ounce</singular> </name>
            </aliases>
            <definition>unit of mass; based on historical US troy weight system (is 1/12 troy pound)</definition>
        </unit>
        <unit>
            <def>3.732417e-1 kg</def>
            <aliases>
                <name> <singular>troy_pound</singular> </name>
                <name> <singular>apothecary_pound</singular> </name>
            </aliases>
            <definition>unit of mass; based on historical US troy weight system (is 5760 grain)</definition>
        </unit>
        <unit>
            <def>20 grain</def>
            <aliases> <name> <singular>scruple</singular> </name> </aliases>
            <definition>unit of mass in apothecaries' weight system (is 1/3 apdram)</definition>
        </unit>
        <unit>
            <def>60 grain</def>
            <aliases> <name> <singular>apdram</singular> </name> </aliases>
            <definition>unit of mass in apothecaries' weight system (is 1/8 apounce)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>avoirdupois_ounce/16</def>
            <aliases>
                <name> <singular>dram</singular> </name>
                <symbol>dr</symbol>
            </aliases>
            <definition>unit of mass in the avoirdupois system (the system commonly used in the United States)</definition>
        </unit>
        <unit>
            <def>480 grain</def>
            <aliases> <name> <singular>apounce</singular> </name> </aliases>
            <definition>unit of mass in apothecaries' weight system (is 1/16 appound)</definition>
        </unit>
        <unit>
            <def>5760 grain</def>
            <aliases> <name> <singular>appound</singular> </name> </aliases>
            <definition>unit of mass in apothecaries' weight system (is same as a troy pound)</definition>
        </unit>
        <unit> 
            <def>94 pound</def>
            <aliases> <name> <singular>bag</singular> </name> </aliases>
            <definition>unit of mass, for a traditional bag of portland cement</definition>
        </unit>
        <unit>
            <def>2000 pound</def>
            <aliases>
                <name> <singular>short_ton</singular> </name>
                <name> <singular>ton</singular> </name>
            </aliases>
            <definition>unit of mass based on US weight system</definition>
        </unit>
        <unit>
            <def>2240 pound</def>
            <aliases>
                <name> <singular>long_ton</singular> </name>
            </aliases>
            <definition>unit of mass based on British imperial weight system</definition>
        </unit>

    <!-- Length -->
        <unit>
            <def>1e-15 m</def>
            <aliases>
                <name> <singular>fermi</singular> </name>
            </aliases>
            <definition>unit of length equal to 10e-15 meters, a typical length-scale of nuclear physics</definition>
        </unit>
        <unit>
            <def>9.46073e15 m</def>
            <aliases>
                <name> <singular>light_year</singular> </name>
            </aliases>
            <definition>unit of length equal to the distance traversed by light in one mean solar year (365.2422 days), a typical length-scale of astronomy</definition>
        </unit>
        <unit>
            <def>1e-6 m</def>
            <aliases>
                <name> <singular>micron</singular> </name>
            </aliases>
            <definition>unit of length, a typical length-scale of technology and science fields</definition>
        </unit>
        <unit>
            <def>2.54e-5 m</def>
            <aliases>
                <name> <singular>mil</singular> </name>
            </aliases>
            <definition>unit of length equal to 0.001 inch, a typical length-scale for measuring wire diameters</definition>
        </unit>
        <unit>
            <def>3.085678e16 m</def>
            <aliases>
                <name> <singular>parsec</singular> </name>
            </aliases>
            <definition>unit of length corresponding to the distance at which the mean radius of the earth's orbit subtends an angle of one second of arc, a typical length-scale of astronomy</definition>
        </unit>
        <unit>
            <def>3.514598e-4 m</def>
            <aliases>
                <name> <singular>printers_point</singular> </name>
            </aliases>
            <definition>unit of length equal to 1/72.27 inch, the original (standardized 1886) unit for measuring font size and other small items on a printed page (see also big_point)</definition>
        </unit>
        <unit>
            <def>2.011684e1 m</def>
            <aliases>
                <name> <singular>chain</singular> </name>
            </aliases>
            <definition>unit of length equal to 66 feet (4 poles), or 1/10 furlong, a typical (historical) scale of land surveying</definition>
        </unit>
        <unit>
            <def>12 printers_point</def>
            <aliases>
                <name> <singular>printers_pica</singular> </name>
                <name> <singular>pica</singular> </name>
            </aliases>
            <definition>unit of length equal to 1/6 inch (12 printers points)</definition>
        </unit>
        <unit>
            <def>nautical_mile</def>
            <aliases>
                <name> <singular>nmile</singular> </name>
            </aliases>
            <definition>unit of length in the US Customary System, equal to 6,076 feet; typically used for air and sea navigation</definition>
        </unit>
        <unit>
            <def>(1200/3937) m</def>
            <aliases>
                <name>
                    <singular>US_survey_foot</singular>
                    <plural>US_survey_feet</plural>
                </name>
            </aliases>
            <definition>unit of length used for earlier survey data in some countries, slightly different than the current international foot</definition>
        </unit>
        <unit>
            <def>3 US_survey_feet</def>
            <aliases>
                <name> <singular>US_survey_yard</singular> </name>
            </aliases>
            <definition>unit of length used in earlier survey data in some countries, slightly different than the current international yard</definition>
        </unit>
        <unit>
            <def>5280 US_survey_feet</def>
            <aliases>
                <name> <singular>US_survey_mile</singular> </name>
                <name> <singular>US_statute_mile</singular> </name>
            </aliases>
            <definition>unit of length used for earlier survey data in some countries, slightly slightly different than the current international mile</definition>
        </unit>
        <unit>
            <def>16.5 US_survey_feet</def>
            <aliases>
                <name> <singular>rod</singular> </name>
                <name> <singular>pole</singular> </name>
                <name> <singular>perch</singular> </name>
            </aliases>
            <definition>unit of length equal to one-fourth of a surveyor's chain</definition>
        </unit>
        <unit>
            <def>660 US_survey_feet</def>
            <aliases> <name> <singular>furlong</singular> </name> </aliases>
            <definition>unit of length equal to 1/8 mile or 10 chains</definition>
        </unit>
        <unit>
            <def>6 US_survey_feet</def>
            <aliases> <name> <singular>fathom</singular> </name> </aliases>
            <definition>unit of length equal to 6 feet in the imperial and US customary systems, typically used for measuring depth of water</definition>
        </unit>
        <unit>
            <def>2.54 cm</def>
            <aliases>
                <name> <singular>international_inch</singular> </name>
                <name> <singular>inch</singular> </name>
                <symbol>in</symbol>
            </aliases>
            <definition>unit of length equal to 25.4 mm by definition, used in imperial and US customary systems</definition>
        </unit>
        <unit>
            <def>12 international_inches</def>
            <aliases>
                <name>
                    <singular>international_foot</singular>
                    <plural>international_feet</plural>
                </name>
                <name>
                    <singular>foot</singular>
                    <plural>feet</plural>
                </name>
                <symbol>ft</symbol>
            </aliases>
            <definition>unit of length equal to 12 international inches, in the imperial and US customary systems; primarily used in the United States</definition>
        </unit>
        <unit>
            <def>3 international_feet</def>
            <aliases>
                <name> <singular>international_yard</singular> </name>
                <name> <singular>yard</singular> </name>
                <symbol>yd</symbol>
            </aliases>
            <definition>unit of length equal to 3 international feet, in the imperial and US customary systems; primarily used in the United States</definition>
        </unit>
        <unit>
            <def>5280 international_feet</def>
            <aliases>
                <name> <singular>international_mile</singular> </name>
                <name> <singular>mile</singular> </name>
                <symbol>mi</symbol>
            </aliases>
            <definition>unit of length equal to 5280 feet, equal to 12 international inches, in the imperial and US customary systems; primarily used in the United States and other smaller countries with ties to the US or United Kingdom</definition>
        </unit>
        <unit>
            <def>inch/72</def>
            <aliases>
                <name> <singular>big_point</singular> </name>
            </aliases>
            <definition>unit of length equal to 1/72 inch, standardized unit in modern computer-based publishing for measuring font size and other small items on a printed page (contrast to printers_point)</definition>
        </unit>
        <unit>
            <def>inch/3</def>
            <aliases>
                <name> <singular>barleycorn</singular> </name>
            </aliases>
            <definition>unit of length based in medieval laws of England and Wales, defining an inch as being 3 barleycorns long (length of a corn of barley); still the basis for current shoe sizes in Great Britain and Ireland</definition>
        </unit>
        <unit>
            <def>191.835 foot</def>
            <aliases>
                <name> <singular>arpentlin</singular> </name>
            </aliases>
            <definition>unit of length in French regions; a linear arpent is of length 10 perch (10 rod)</definition>
        </unit>

    <!-- Angular Velocity -->
        <unit>
            <comment>exact</comment>
            <def>rotation/second</def>
            <aliases>
                <name>
                    <singular>rotation_per_second</singular>
                    <plural>rotations_per_second</plural>
                </name>
                <symbol>rps</symbol>
                <symbol>cps</symbol>
            </aliases>
            <definition>unit of angular velocity</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>rotation/minute</def>
            <aliases> <symbol>rpm</symbol> </aliases>
            <definition>unit of angular velocity measuring the angular distance covered by a rotating object, divided by the amount of time used to cover that distance; measured perpendicular to the plane of rotation, with direction usually indicated by the right-hand rule</definition>
        </unit>

    <!-- Lineic Mass -->
        <unit>
            <def>1.111111e-7 kg/m</def>
            <aliases>
                <name> <singular>denier</singular> </name>
            </aliases>
            <definition>unit of lineic mass density for fibers, equal to the mass in grams per 9000 meters (more common in United States and United Kingdom); a single strand of silk is approximately one denier</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-6 kg/m</def>
            <aliases>
                <name> <singular>tex</singular> </name>
            </aliases>
            <definition>unit of lineic mass density for fibers, defined as mass in grams per 1000 meters (more common in Canada and Continental Europe)</definition>
        </unit>

    <!-- Mass per unit time (includes flow) -->
        <unit>
            <def>5.72135e-11 kg/(Pa.s.m^2)</def>
            <aliases>
                <name>
                    <singular>perm_0C</singular>
                    <plural>perms_0C</plural>
                </name>
            </aliases>
            <definition>unit of mass per unit time (includes flow) for how fast water vapor flows through substance, or permeance; equals 1 gram of water vapor per hour, per square meter, per millimeter of mercury at 0 degrees C</definition>
        </unit>
        <unit>
            <def>5.74525e-11 kg/(Pa.s.m^2)</def>
            <aliases>
                <name>
                    <singular>perm_23C</singular>
                    <plural>perms_23C</plural>
                </name>
            </aliases>
            <definition>unit of mass per unit time for how fast water vapor flows through substance, or permeance; equals 1 gram of water vapor per hour, per square meter, per millimeter of mercury at 23 degrees C</definition>
        </unit>

    <!-- Area -->
        <unit>
            <def>5.067075e-10 m^2</def>
            <aliases>
                <name> <singular>circular_mil</singular> </name>
            </aliases>
            <definition>unit of area equal to the area of a one-mil diameter circle</definition>
        </unit>
        <unit>
            <comment>porous solid permeability</comment>
            <def>9.869233e-13 m^2</def>
            <aliases> <name> <singular>darcy</singular> </name> </aliases>
            <definition>unit of area for measuring permeability to fluid, equal to 1 cubic centimeter of fluid with 1 centipoise viscosity in 1 second through a 1-square-centimeter cross section of porous medium 1 centimeter long at 1 atmosphere</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>160 rod^2</def>
            <aliases>
                <name> <singular>acre</singular> </name>
            </aliases>
            <definition>unit of area in the US Customary System, used in land and sea floor measurement, equal to 43560 square feet</definition>
        </unit>

    <!-- Volume -->
        <unit>
            <comment>An "acre.foot", however, is 1233.4867714897 m^3.  Odd.</comment>
            <def>1.233489e3 m^3</def>
            <aliases>
                <name>
                    <singular>acre_foot</singular>
                    <plural>acre_feet</plural>
                </name>
            </aliases>
            <definition>unit of volume used to describe large-scale water resources in the United State; equal to the volume of one acre of surface area with one foot of depth depth</definition>
        </unit>
        <unit>
            <def>2.359737e-3 m^3</def>
            <aliases>
                <name>
                    <singular>board_foot</singular>
                    <plural>board_feet</plural>
                </name>
            </aliases>
            <definition>unit of volume equal to the cubic contents of a piece of lumber one foot square and one inch thick, used in measuring logs and lumber in the United States and Canada</definition>
        </unit>
        <unit>
            <def>3.523907e-2 m^3</def>
            <aliases>
                <name> <singular>bushel</singular> </name>
                <symbol>bu</symbol>
            </aliases>
            <definition>unit of volume defined as 2150.42 cubic inches or 4 pecks in the US Customary system (and formerly in England), where it is used as a dry measure</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>bushel/4</def>
            <aliases>
                <name> <singular>peck</singular> </name>
                <symbol>pk</symbol>
            </aliases>
            <definition>unit of volume defined as 537.6 cubic inches  in the US Customary system (and formerly in England), where it is used as a dry measure</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.546090e-3 m^3</def>
            <aliases>
                <name> <singular>Canadian_liquid_gallon</singular> </name>
            </aliases>
            <definition>unit of volume for liquids in the Imperial system</definition>
        </unit>
        <unit>
            <def>4.404884e-3 m^3</def>
            <aliases>
                <name> <singular>US_dry_gallon</singular> </name>
            </aliases>
            <definition>unit of volume for dry measure in the US Customary system, defined as 1/2 peck or 1/8 bushel</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>cm^3</def>
            <aliases> <symbol>cc</symbol> </aliases>
            <definition>unit of volume equal to the volume of a cube 1 centimeter on each side</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1 m^3</def>
            <aliases>
                <name> <singular>stere</singular> </name>
            </aliases>
            <definition>unit of volume equal to a cubic meter, originally defined primarily as a measure for firewood</definition>
        </unit>
        <unit>
            <def>2.831685 m^3</def>
            <aliases>
                <name> <singular>register_ton</singular> </name>
            </aliases>
            <definition>unit of volume used for internal capacity of ships, equal to 100 cubic feet</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_dry_gallon/4</def>
            <aliases>
                <name> <singular>US_dry_quart</singular> </name>
                <name> <singular>dry_quart</singular> </name>
            </aliases>
            <definition>unit of volume for dry measure in the US Customary system, equal to 1/32 US bushel</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_dry_gallon/8</def>
            <aliases>
                <name> <singular>US_dry_pint</singular> </name>
                <name> <singular>dry_pint</singular> </name>
            </aliases>
            <definition>unit of volume for dry measure in the US Customary system, equal to 1/2 US dry quart</definition>
        </unit>
        <unit>
            <def>3.785412e-3 m^3</def>
            <aliases>
                <name> <singular>US_liquid_gallon</singular> </name>
                <name> <singular>liquid_gallon</singular> </name>
                <name> <singular>gallon</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, defined as 3.785412 liters</definition>
        </unit>
        <unit>
            <comment>The following is the definition of the petroleum industry</comment>
            <def>42 US_liquid_gallon</def>
            <aliases>
                <name> <singular>barrel</singular> </name>
                <symbol>bbl</symbol>
            </aliases>
            <definition>unit of volume used by US and Canadian petroleum organizations</definition>
        </unit>
        <unit>
            <comment>The following is exact regardless of the definition of "barrel"</comment>
            <def>barrel/4</def>
            <aliases>
                <name> <singular>firkin</singular> </name>
            </aliases>
            <definition>unit of volume whose exact quantity depends on the type of barrel on which it is defined; in this table it is defined based on the oil barrel used by the petroleum industry</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_liquid_gallon/4</def>
            <aliases>
                <name> <singular>US_liquid_quart</singular> </name>
                <name> <singular>liquid_quart</singular> </name>
                <name> <singular>quart</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/4 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_liquid_gallon/8</def>
            <aliases>
                <name> <singular>US_liquid_pint</singular> </name>
                <name> <singular>liquid_pint</singular> </name>
                <name> <singular>pint</singular> </name>
                <symbol>pt</symbol>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/8 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_liquid_gallon/16</def>
            <aliases>
                <name> <singular>US_liquid_cup</singular> </name>
                <name> <singular>liquid_cup</singular> </name>
                <name> <singular>cup</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/16 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_liquid_gallon/32</def>
            <aliases>
                <name> <singular>US_liquid_gill</singular> </name>
                <name> <singular>liquid_gill</singular> </name>
                <name> <singular>gill</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/32 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_liquid_gallon/128</def>
            <aliases>
                <name> <singular>US_fluid_ounce</singular> </name>
                <name> <singular>US_liquid_ounce</singular> </name>
                <name> <singular>fluid_ounce</singular> </name>
                <name> <singular>liquid_ounce</singular> </name>
                <symbol>oz</symbol>
                <symbol>floz</symbol>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/128 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_fluid_ounce/2</def>
            <aliases>
                <name> <singular>tablespoon</singular> </name>
                <symbol>Tbl</symbol>
                <symbol>Tbsp</symbol>
                <symbol>tbsp</symbol>
                <symbol>Tblsp</symbol>
                <symbol>tblsp</symbol>
            </aliases>
            <definition>unit of volume for liquid measure in the US Customary system, equal to 1/2 liquid ounce</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>US_fluid_ounce/8</def>
            <aliases>
                <name> <singular>fluid_dram</singular> </name>
                <symbol>fldr</symbol>
            </aliases>
            <definition>unit of volume for liquid measure in the apothecary system, equal to 1/8 liquid ounce</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>tablespoon/3</def>
            <aliases>
                <name> <singular>teaspoon</singular> </name>
                <symbol>tsp</symbol>
            </aliases>
            <definition>unit of volume defined as 1/3 tablespoon, the actual volume of which can vary depending on the measurement system (but is based on the US Customary system in this database)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.546090e-3 m^3</def>
            <aliases>
                <name> <singular>UK_liquid_gallon</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>UK_liquid_gallon/4</def>
            <aliases>
                <name> <singular>UK_liquid_quart</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system, equal to 1/4 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>UK_liquid_gallon/8</def>
            <aliases>
                <name> <singular>UK_liquid_pint</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system, equal to 1/8 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>UK_liquid_gallon/16</def>
            <aliases>
                <name> <singular>UK_liquid_cup</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system, equal to 1/16 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>UK_liquid_gallon/32</def>
            <aliases>
                <name> <singular>UK_liquid_gill</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system, equal to 1/32 liquid gallon</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>UK_liquid_gallon/160</def>
            <aliases>
                <name> <singular>UK_fluid_ounce</singular> </name>
                <name> <singular>UK_liquid_ounce</singular> </name>
            </aliases>
            <definition>unit of volume for liquid measure in the Imperial system, equal to 1/160 liquid gallon</definition>
        </unit>
        <unit>
            <def>lg(re (1e-6 m)^3)</def>
            <aliases> <symbol>BZ</symbol> </aliases>
            <definition>logarithmic unit used to compare the reflectivity (Z) of an unknown remote object, to the reflective return created by a droplet of rain with a diameter of 1 mm; is the base unit for "dBz", which is the typical logarithmic unit for measuring atmospheric radar reflectivity; a value of 0 Bz (0 DBz) corresponds to the return from a single cubic micron; a value of 6 Bz (60 DBz) corresponds to extremely heavy rain.</definition>
        </unit>

    <!-- Time -->
        <unit>
            <def>1e-8 s</def>
            <aliases> <name> <singular>shake</singular> </name> </aliases>
            <definition>unit of time approximating the lifetime of an individual neutron, useful for describing very brief durations, e.g., in nuclear physics</definition>
        </unit>
        <unit>
            <def>8.616409e4 s</def>
            <aliases>
                <name> <singular>sidereal_day</singular> </name>
            </aliases>
            <definition>unit of time that it takes the earth to complete one revolution with respect to a star, roughly 23 hours, 56 minutes, 4 seconds</definition>
        </unit>
        <unit>
            <def>3.590170e3 s</def>
            <aliases>
                <name> <singular>sidereal_hour</singular> </name>
            </aliases>
            <definition>unit of time equal to 1/24 sidereal day</definition>
        </unit>
        <unit>
            <def>5.983617e1 s</def>
            <aliases>
                <name> <singular>sidereal_minute</singular> </name>
            </aliases>
            <definition>unit of time equal to 1/60 sidereal hour</definition>
        </unit>
        <unit>
            <def>0.9972696 s</def>
            <aliases>
                <name> <singular>sidereal_second</singular> </name>
            </aliases>
            <definition>unit of time equal to 1/60 sidereal second</definition>
        </unit>
        <unit>
            <def>3.155815e7 s</def>
            <aliases>
                <name> <singular>sidereal_year</singular> </name>
            </aliases>
            <definition>unit of time for the earth to make one complete revolution around the sun, relative to the fixed stars</definition>
        </unit>
        <unit>
            <def>3.15569259747e7 s</def>
            <aliases>
                <name> <singular>tropical_year</singular> </name>
                <name> <singular>year</singular> </name>
                <!-- The following is commented-out because "a" already maps to "are"
                <symbol>a</symbol>
                -->
                <symbol>yr</symbol>
            </aliases>
            <definition>unit of time; Interval between 2 successive passages of sun through vernal equinox (365.242198781 days). See http://www.ast.cam.ac.uk/pubinfo/leaflets/, http://aa.usno.navy.mil/AA/, and http://adswww.colorado.edu/adswww/astro_coord.html</definition>
        </unit>
        <unit>
            <def>29.530589 day</def>
            <aliases>
                <name> <singular>lunar_month</singular> </name>
            </aliases>
            <definition>unit of time equal to the average time between successive new or full moons; equal to approximately 29 days, 12 hours, 44 minutes</definition>
        </unit>
        <unit>
            <def>365 day</def>
            <aliases>
                <name> <singular>common_year</singular> </name>
            </aliases>
            <definition>unit of time corresponding to a 'normal' calendar year, that is, one without insertion of a leap day</definition>
        </unit>
        <unit>
            <def>366 day</def>
            <aliases>
                <name> <singular>leap_year</singular> </name>
            </aliases>
            <definition>unit of time corresponding to a calendar year with a leap day inserted</definition>
        </unit>
        <unit>
            <def>365.25 day</def>
            <aliases>
                <name> <singular>Julian_year</singular> </name>
            </aliases>
            <definition>unit of time recognized by the International Astronomical Union for use in astronomy, defined as 365.25 days of 86400 seconds</definition>
        </unit>
        <unit>
            <def>365.2425 day</def>
            <aliases>
                <name> <singular>Gregorian_year</singular> </name>
            </aliases>
            <definition>unit of time based on the Gregorian Calendar, the one commonly used today; approximates the tropical year as 365 + 97/400 days</definition>
        </unit>
        <unit>
            <def>27.321661 day</def>
            <aliases>
                <name> <singular>sidereal_month</singular> </name>
            </aliases>
            <definition>unit of time based on 1/12 of the sidereal year</definition>
        </unit>
        <unit>
            <def>27.321582 day</def>
            <aliases>
                <name> <singular>tropical_month</singular> </name>
            </aliases>
            <definition>unit of time based on 1/12 of the tropical year</definition>
        </unit>
        <unit>
            <def>14 day</def>
            <aliases>
                <name> <singular>fortnight</singular> </name>
            </aliases>
            <definition>unit of time commonly defined as 14 days</definition>
        </unit>
        <unit>
            <def>7 day</def>
            <aliases> <name> <singular>week</singular> </name> </aliases>
            <definition>unit of time commonly defined as 7 days</definition>
        </unit>
        <unit>
            <comment>multiple values have been proposed for the amount of time represented by a 'jiffy'</comment>
            <def>0.01 s</def>
            <aliases> <name> <singular>jiffy</singular> </name> </aliases>
            <definition>unit of time used in computer animation as a method of defining playback rate</definition>
        </unit>
        <unit>
            <def>1e9 year</def>
            <aliases> <name> <singular>eon</singular> </name> </aliases>
            <definition>unit of time defined in astronomy as 1 billion years</definition>
        </unit>
        <unit>
            <def>year/12</def>
            <aliases> <name> <singular>month</singular> </name> </aliases>
            <definition>unit of time defined as the average length of time for a calendar month</definition>
        </unit>

    <!-- Volume per time -->
        <unit>
            <comment>exact</comment>
            <def>1e6 m^3/s</def>
            <aliases>
                <name> <singular>sverdrup</singular> </name>
                <!-- The following is commented-out because "Sv" means
                     "sievert" in the SI unit-system.
                <symbol>Sv</symbol>
                -->
            </aliases>
            <definition>unit of volume transport, used almost exclusively to measure the volumetric rate of ocean currents</definition>
        </unit>

    <!-- Acceleration -->
        <unit>
            <comment>exact</comment>
            <def>9.806650 m/s^2</def>
            <aliases>
                <name> <singular>standard_free_fall</singular> </name>
            </aliases>
            <definition>unit of acceleration corresponding to the nominal gravitational acceleration of an object in a vacuum near the surface of earth</definition>
        </unit>
        <unit>
            <comment>should be local</comment>
            <def>standard_free_fall</def>
            <aliases> <name> <singular>gravity</singular> </name> </aliases>
            <definition>unit of acceleration synonymous with standard rate of free fall (in earth's gravity)</definition>
        </unit>

    <!-- Some "units" that make subsequent definitions easier -->
        <unit>
            <comment>exact</comment>
            <def>gravity 1000 kg/m^3</def>
            <aliases>
                <name> <singular>conventional_water</singular> </name>
                <name> <singular>water</singular> </name>
                <symbol>H2O</symbol>
                <symbol>h2o</symbol>
            </aliases>
            <definition>specifies the acceleration at the earth's surface of a substance with the density of water</definition>
        </unit>
        <unit>
            <def>gravity 999.972 kg/m^3</def>
            <aliases>
                <name>
                    <singular>water_4C</singular>
                    <plural>waters_4C</plural>
                </name>
                <name>
                    <singular comment="actually 39.2 F">water_39F</singular>
                    <plural>waters_39F</plural>
                </name>
            </aliases>
            <definition>specifies the acceleration at the earth's surface of a substance with the density of water at 4 degrees C</definition>
        </unit>
        <unit>
            <def>gravity 999.001 kg/m^3</def>
            <aliases>
                <name>
                    <singular>water_60F</singular>
                    <plural>waters_60F</plural>
                </name>
            </aliases>
            <definition>specifies the acceleration at the earth's surface of a substance with the density of water at 60 degrees F</definition>
        </unit>
        <unit>
            <def>gravity 13595.10 kg/m^3</def>
            <aliases>
                <name>
                    <singular>mercury_0C</singular>
                    <plural>mercuries_0C</plural>
                </name>
                <name>
                    <singular>mercury_32F</singular>
                    <plural>mercuries_32F</plural>
                </name>
                <name>
                    <singular>conventional_mercury</singular>
                    <plural>conventional_mercuries</plural>
                </name>
                <symbol>Hg</symbol>
            </aliases>
            <definition>specifies the acceleration at the earth's surface of a substance with the density of mercury at 0 degrees C</definition>
        </unit>
        <unit>
            <def>gravity 13556.8 kg/m^3</def>
            <aliases>
                <name>
                    <singular>mercury_60F</singular>
                    <plural>mercuries_60F</plural>
                </name>
            </aliases>
            <definition>specifies the acceleration at the earth's surface of a substance with the density of mercury at 60 degrees F</definition>
        </unit>

    <!-- Force -->
        <unit>
            <def>standard_free_fall</def>
            <aliases> <name> <singular>force</singular> </name> </aliases>
            <definition>unit of force equivalent to the force generated by the effect of gravity</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-5 N</def>
            <aliases> <name> <singular>dyne</singular> </name> </aliases>
            <definition>unit of force, equal to the force that produces an acceleration of one centimeter per second per second on a mass of one gram (the standard centimeter-gram-second unit of force)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>9.806650e-3 N</def>
            <aliases> <name> <singular>pond</singular> </name> </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one gram of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>9.806650 N</def>
            <aliases>
                <name> <singular>force_kilogram</singular> </name>
                <name>
                    <singular>kilogram_force</singular>
                    <plural>kilograms_force</plural>
                </name>
                <symbol>kgf</symbol>
            </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one kilogram of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>2.780139e-1 N</def>
            <aliases>
                <name> <singular>force_ounce</singular> </name>
                <name>
                    <singular>ounce_force</singular>
                    <plural>ounces_force</plural>
                </name>
                <symbol>ozf</symbol>
            </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one ounce of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.4482216152605 N</def>
            <aliases>
                <name> <singular>force_pound</singular> </name>
                <name>
                    <singular>pound_force</singular>
                    <plural>pounds_force</plural>
                </name>
                <symbol>lbf</symbol>
            </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one pound of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1.382550e-1 N</def>
            <aliases>
                <name> <singular>poundal</singular> </name>
            </aliases>
            <definition>unit of force, that which is necessary to accelerate 1 pound-mass to 1 foot per second per second</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>gram force</def>
            <aliases>
                <name>
                    <singular>gram_force</singular>
                    <plural>grams_force</plural>
                </name>
                <name>
                    <singular>force_gram</singular>
                </name>
                <symbol>gf</symbol>
            </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one gram of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>2000 force_pound</def>
            <aliases>
                <name> <singular>force_ton</singular> </name>
                <name>
                    <singular>ton_force</singular>
                    <plural>tons_force</plural>
                </name>
            </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one ton of mass in a 9.80665 m/s2 gravitational field (specifically a short ton of mass)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1000 lbf</def>
            <aliases> <name><singular>kip</singular></name> </aliases>
            <definition>unit of force, equal to the magnitude of the force exerted by one thousand pounds of mass in a 9.80665 m/s2 gravitational field</definition>
        </unit>

    <!-- Pressure, Stress -->
        <unit>
            <comment>exact</comment>
            <def>1.01325e5 Pa</def>
            <aliases>
                <name> <singular>standard_atmosphere</singular> </name>
                <name> <singular>atmosphere</singular> </name>
                <symbol>atm</symbol>
            </aliases>
            <definition>unit of pressure, an international reference pressure intended to represent the mean atmospheric pressure at mean sea level at the latitude of Paris, France</definition>
        </unit>
        <unit>
            <comment>exact; note that the symbol 'at' clashes with that of the katal ('kat'), the SI unit of catalytic activity</comment>
            <def>1 kg gravity/cm2</def>
            <aliases>
                <name> <singular>technical_atmosphere</singular> </name>
                <symbol>at</symbol>
            </aliases>
            <definition>unit of pressure equal to one kilogram force per square centimeter</definition>
        </unit>
        <unit>
            <def>cm H2O</def>
            <aliases>
                <symbol>cm_H2O</symbol>
                <symbol>cmH2O</symbol>
            </aliases>
            <definition>unit of pressure derived from pressure head calculations using metrology; represents the pressure exerted by a column of water of 1 cm height at 4 degrees C</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>inch water_39F</def>
            <aliases>
                <name>
                    <singular>inch_H2O_39F</singular>
                    <plural>inches_H2O_39F</plural>
                </name>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of water of 1 inch height at 39 degrees F</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>inch water_60F</def>
            <aliases>
                <name>
                    <singular>inch_H2O_60F</singular>
                    <plural>inches_H2O_60F</plural>
                </name>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of water of 1 inch height at 60 degrees F</definition>
        </unit>
        <unit>
            <def>foot water</def>
            <aliases>
                <name>
                    <singular>foot_water</singular>
                    <plural>feet_water</plural>
                </name>
                <name>
                    <singular>foot_H2O</singular>
                    <plural>feet_H2O</plural>
                </name>
                <name>
                    <singular>footH2O</singular>
                    <plural>feetH2O</plural>
                </name>
                <symbol>ftH2O</symbol>
                <symbol>fth2o</symbol>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of water of 1 foot height at 4 degrees C</definition>
        </unit>
        <unit>
            <def>cm Hg</def>
            <aliases>
                <symbol>cm_Hg</symbol>
                <symbol>cmHg</symbol>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 cm height at 0 degrees C</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>mm mercury_0C</def>
            <aliases>
                <name>
                    <singular>millimeter_Hg_0C</singular>
                    <plural>millimeters_Hg_0C</plural>
                </name>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 mm height at 0 degrees C</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>inch mercury_32F</def>
            <aliases>
                <name>
                    <singular>inch_Hg_32F</singular>
                    <plural>inches_Hg_32F</plural>
                </name>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 inch height at 32 degrees F</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>inch mercury_60F</def>
            <aliases>
                <name>
                    <singular>inch_Hg_60F</singular>
                    <plural>inches_Hg_60F</plural>
                </name>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 inch height at 60 degrees F</definition>
        </unit>
        <unit>
            <def>mm Hg</def>
            <aliases>
                <name>
                    <singular>millimeter_Hg</singular>
                    <plural>millimeters_Hg</plural>
                </name>
                <name> <singular>torr</singular> </name>
                <symbol>mm_Hg</symbol>
                <symbol>mm_hg</symbol>
                <symbol>mmHg</symbol>
                <symbol>mmhg</symbol>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 mm height at 0 degrees C; approximately (within 0.000015%, generally below measurement error) 1 Torr, which is 1/760 standard atmospheric pressure</definition>
        </unit>
        <unit>
            <def>inch Hg</def>
            <aliases>
                <name>
                    <singular>inch_Hg</singular>
                    <plural>inches_Hg</plural>
                </name>
                <symbol>in_Hg</symbol>
                <symbol>inHg</symbol>
            </aliases>
            <definition>unit of pressure representing the pressure exerted by a column of mercury of 1 inch height at 0 degrees C</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1 pound gravity/in^2</def>
            <aliases> <symbol>psi</symbol> </aliases>
            <definition>unit of pressure representing the pressure exerted, due to gravity, by a one-pound mass, of area one square inch; commonly referred to as "pounds per square inch"</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>kip/in^2</def>
            <aliases> <symbol>ksi</symbol> </aliases>
            <definition>unit of pressure representing the pressure exerted, due to gravity, by a 1000-pound mass, of area one square inch</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>0.1 N/m^2</def>
            <aliases>
                <name> <singular>barie</singular> </name>
                <name> <singular>barye</singular> </name>
            </aliases>
            <definition>unit of pressure equal to one dyne per square centimeter</definition>
        </unit>
        <unit>
            <comment>sound pressure level</comment>
            <def>lg(re 20e-6 Pa)</def>
            <aliases> <symbol>B_SPL</symbol> </aliases>
            <definition>logarithmic unit used to compare the sound pressure of an unknown sound to a standard reference sound pressure; is the base unit for "dB_SPL", a more typical logarithmic unit for measuring sound pressure (the SI unit for sound pressure is pascal); the standard reference sound pressure in air or other gases is 20 microPascal, which is usually considered the threshold of human hearing (at 1 kHz)</definition>
        </unit>

    <!-- Viscosity -->
        <unit>
            <comment>exact</comment>
            <def>1e-1 Pa.s</def>
            <aliases>
                <name> <singular>poise</singular> </name>
            </aliases>
            <definition>unit of dynamic viscosity, corresponding to 0.1 pascal-second (pascal-second: a fluid placed between two plates, when one plate is pushed sideways with a shear stress of one pascal, moves a distance equal to the thickness of the layer between the plates in one second)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-4 m^2/s</def>
            <aliases>
                <name> <singular>stokes</singular> </name>
                <symbol>St</symbol>
            </aliases>
            <definition>unit of kinematic viscosity, measuring the ratio of the dynamic viscosity to the density of the fluid; water at 20 degrees C has a kinematic viscosity about 100 stokes, or more cmomonly, 1 cSt</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>10/(Pa.s)</def>
            <aliases> <name> <singular>rhe</singular> </name> </aliases>
            <definition>unit of fluidity (reciprocal of velocity), measured in reciprocal poise</definition>
        </unit>

    <!-- Energy, Work, Quantity of Heat -->
        <unit>
            <comment>exact</comment>
            <def>1e-7 J</def>
            <aliases> <name> <singular>erg</singular> </name> </aliases>
            <definition>unit of work, equal to the amount of work done by a force of one dyne exerted for a distance of one centimeter (in CGS base units, one gram centimeter-squared per second-squared)</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1.05505585262e3 J</def>
            <aliases>
                <name>
                    <singular>IT_Btu</singular>
                    <plural>IT_Btus</plural>
                </name>
                <name>
                    <singular>Btu</singular>
                    <plural>Btus</plural>
                </name>
            </aliases>
            <definition>unit of energy, equal to the energy needed to cool or heat one pound of water by one degree F; this uses the International Steam Table (IT) calorie , defined by the Fifth International Conference on the properties of Steam (1956)</definition>
        </unit>
        <unit>
            <comment>exact (reference NIST Guide to SI Units)</comment>
            <def>1.05506e8 J</def>
            <aliases>
                <name> <singular>EC_therm</singular> </name>
            </aliases>
            <definition>unit of energy legally defined by the Council Directive of 20 December 1979, Council of the European Communities (now the European Union, EU);.roughly equal to 100,000 IT_Btu </definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.184000 J</def>
            <aliases>
                <name> <singular>thermochemical_calorie</singular> </name>
            </aliases>
            <definition>unit of heat energy defined as 4.184 Joules exactly (International Standard ISO 31-4: Quantities and units, Part 4: Heat); approximately the energy needed to increase the temperature of 1 gram of water by 1 C</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.1868 J</def>
            <aliases>
                <name> <singular>IT_calorie</singular> </name>
                <name> <singular>calorie</singular> </name>
                <symbol>cal</symbol>
            </aliases>
            <definition>unit of heat energy used in thermochemistry, the International Steam Table (IT) calorie defined by the Fifth International Conference on the properties of Steam (1956)</definition>
        </unit>
        <unit>
            <comment>by definition</comment>
            <def>4.184 MJ/kg</def>
            <aliases>
                <name> <singular>TNT</singular><noplural/></name>
            </aliases>
            <definition>unit of energy; approximately the energy released by the detonation of a given amount of mass of TNT</definition>
        </unit>
        <unit>
            <comment>by definition</comment>
            <def>4.184e9 J</def>
            <aliases>
                <name>
                    <singular>ton_TNT</singular>
                    <plural>tons_TNT</plural>
                </name>
            </aliases>
            <definition>unit of energy; approximately the energy released by the detonation of a 1000 kilograms of TNT</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1.054804e8 J</def>
            <aliases>
                <name> <singular>US_therm</singular> </name>
                <name> <singular>therm</singular> </name>
                <symbol>thm</symbol>
            </aliases>
            <definition>unit of energy legally defined in the U.S. Federal Register of July 27, 1968, and the legal unit used by the U.S. natural gas industry</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>watt.hour</def>
            <aliases>
                <name> <singular>watthour</singular> </name>
            </aliases>
            <definition>unit of energy equal to the product of the power in watts and the time in hours (if the energy is being transmitted or used at a constant rate (power) over a period of time); one watt is equal to 1 Joule/second</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e9 eV</def>
            <aliases> <symbol>bev</symbol> </aliases>
            <definition>unit of energy corresponding to 1 billion electron volts (eV)</definition>
        </unit>

    <!-- Power, Radiant Flux -->
        <unit>
            <comment>exact</comment>
            <def>V.A</def>
            <aliases>
                <name> <singular>voltampere</singular> </name>
                <symbol>VA</symbol>
            </aliases>
            <definition>unit of electric power equal to the product of one volt and one ampere, equivalent to one watt for direct current systems and a unit of apparent power for alternating current systems</definition>
        </unit>
        <unit>
            <def>9.80950e3 W</def>
            <aliases>
                <name> <singular>boiler_horsepower</singular> </name>
            </aliases>
            <definition>unit of power equal to the power required to evaporate 34.5 lb of fresh water at 212 degrees F in one hour; describes a boiler's capacity to deliver steam to a steam engine</definition>
        </unit>
        <unit>
            <comment>shaft_horsepower is a unit of power as delivered by a drive shaft at its output (e.g., of a ship, aircraft engine, or helicopter rotor; typically not automobiles due to drive train losses)</comment>
            <def>7.456999e2 W</def>
            <aliases>
                <name> <singular>shaft_horsepower</singular> </name>
                <name> <singular>horsepower</singular> </name>
                <symbol>hp</symbol>
            </aliases>
            <definition>unit of power originally corresponding to the estimated typical power of draft horses, calculated as lifting 33000 pounds one foot in one minute (550 foot-pounds/second)</definition>
        </unit>
        <unit>
            <def>7.35499e2 W</def>
            <aliases>
                <name> <singular>metric_horsepower</singular> </name>
            </aliases>
            <definition>unit of power corresponding to a calculation of 75 kilogram-meters/second</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>7.460000e2 W</def>
            <aliases>
                <name> <singular>electric_horsepower</singular> </name>
            </aliases>
            <definition>unit of power defined in the International System of Units as exactly 746 W; generally used for power used by electrical machines</definition>
        </unit>
        <unit>
            <def>7.46043e2 W</def>
            <aliases>
                <name> <singular>water_horsepower</singular> </name>
            </aliases>
            <definition>unit of power used in the U.S. primarily in rating pumps; calculated as pump capacity Q (gallons per minute) times pump pressure ("head") of P (feet of head), divided by 3956 water horsepower; the calculation assumes water density is 8 1/3 pounds per U.S. gallon, which is not exact.</definition>
        </unit>
        <unit>
            <def>7.4570e2 W</def>
            <aliases>
                <name> <singular>UK_horsepower</singular> </name>
            </aliases>
            <definition>unit of power originally corresponding to the estimated typical power of draft horses, calculated as lifting 33000 pounds one foot in one minute (550 foot-pounds/second), as calculated/specified in the United Kingdom</definition>
        </unit>
        <unit>
            <def>12000 Btu/hr</def>
            <aliases>
                <name> <singular>refrigeration_ton</singular> </name>
                <name>
                    <singular>ton_of_refrigeration</singular>
                    <plural>tons_of_refrigeration</plural>
                </name>
            </aliases>
            <definition>unit of power describing the heat-extraction capacity of cooling equipment; defined as the heat absorbed by melting 1 short ton of pure ice at 0 degrees C in 24 hours</definition>
        </unit>
        <unit>
            <def>lg(re 1 W)</def>
            <aliases> <symbol>BW</symbol> </aliases>
            <definition>unit of power in decibel scale, referenced to 1 watt; the power in bel-watts is equal to 100 times the base 10 logarithm of the power in watts (making decibel-watt, the more common term, 10 times the base 10 log of the power in watts)</definition>
        </unit>
        <unit>
            <def>lg(re 1 mW)</def>
            <aliases> <symbol>Bm</symbol> </aliases>
            <definition>unit of power in decibel scale, referenced to 1 milliwatt; the power in bel-milliwatts is equal to 100 times the base 10 logarithm of the power in milliwatts (making decibel-milliwatt, the more common term, 10 times the base 10 log of the power in watts)</definition>
        </unit>

    <!-- Heat -->
        <unit>
            <def>1.55e-1 K.m^2/W</def>
            <aliases> <name> <singular>clo</singular> </name> </aliases>
            <definition>unit of thermal resistance used in describing the insulating value of clothing; the amount of thermal resistance needed to maintain in comfort a resting subject in a normally ventilated room (air movement 10 cm/sec) at a temperature of 20 degrees C and a humidity less than 50%</definition>
        </unit>

    <!-- Electricity and Magnetism -->
        <unit>
            <def>10 A</def>
            <aliases> <name><singular>abampere</singular></name> </aliases>
            <definition>basic unit of electricity in the electromagnetic CGS system of units</definition>
        </unit>
        <unit>
            <def>7.957747e-1 A</def>
            <aliases> <name><singular>gilbert</singular></name> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>3.335640e-10 A</def>
            <aliases>
                <name><singular>statampere</singular></name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>10 A</def>
            <aliases> <name><singular>biot</singular></name> </aliases>
            <definition>basic unit of electricity in the electromagnetic CGS system of units (same as abampere), named after Jean-Baptiste Biot</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e9 F</def>
            <aliases> <name> <singular>abfarad</singular> </name> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-9 H</def>
            <aliases>
                <name> <singular>abhenry</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e9 S</def>
            <aliases> <name> <singular>abmho</singular> </name> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-9 ohm</def>
            <aliases> <name> <singular>abohm</singular> </name> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-8 V</def>
            <aliases> <name> <singular>abvolt</singular> </name> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>1.602176487e-19 C</def>
            <aliases> <symbol>e</symbol> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>9.64957e4 C</def>
            <aliases>
                <name> <singular>chemical_faraday</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>9.65219e4 C</def>
            <aliases>
                <name> <singular>physical_faraday</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>9.648531e4 C</def>
            <aliases>
                <name> <singular>C12_faraday</singular> </name>
                <name> <singular>faraday</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-9 T</def>
            <aliases>
                <name> <singular>gamma</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-4 T</def>
            <aliases>
                <name> <singular>gauss</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-8 Wb</def>
            <aliases>
                <name> <singular>maxwell</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>7.957747e1 A/m</def>
            <aliases>
                <name> <singular>oersted</singular> </name>
                <symbol>Oe</symbol>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>3.335640e-10 C</def>
            <aliases>
                <name> <singular>statcoulomb</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>1.112650e-12 F</def>
            <aliases>
                <name> <singular>statfarad</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>8.987554e11 H</def>
            <aliases>
                <name> <singular>stathenry</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>1.112650e-12 S</def>
            <aliases>
                <name> <singular>statmho</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>8.987554e11 ohm</def>
            <aliases>
                <name> <singular>statohm</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>2.997925e2 V</def>
            <aliases>
                <name> <singular>statvolt</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>1.256637e-7 Wb</def>
            <aliases>
                <name> <singular>unit_pole</singular> </name>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>lg(re 1 V)</def>
            <aliases> <symbol>BV</symbol> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <comment>rms voltage</comment>
            <def>lg(re 0.775 V)</def>
            <aliases> <symbol>Bv</symbol> </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>
        <unit>
            <def>lg(re 1e-6 V)</def>
            <aliases> 
                <symbol comment="uses MICRO SIGN">B&#xB5;V</symbol>
            </aliases>
            <definition>unit of electricity/magnetism</definition>
        </unit>

    <!-- Thermodynamic Temperature -->
        <unit>
            <def>K/1.8</def>
            <aliases>
                <symbol comment="DEGREE SIGN">&#xB0;R</symbol>    
                <name>
                    <singular>degree_rankine</singular>
                    <plural>degrees_rankine</plural>
                </name>
                <name>
                    <singular>degreeR</singular>
                    <plural>degreesR</plural>
                </name>
                <name>
                    <singular>degree_R</singular>
                    <plural>degrees_R</plural>
                </name>
                <name>
                    <singular>degR</singular>
                    <plural>degsR</plural>
                </name>
                <name>
                    <singular>deg_R</singular>
                    <plural>degs_R</plural>
                </name>
            </aliases>
            <definition>unit of thermodynamic temperature</definition>
        </unit>
        <unit>
            <def>&#xB0;R @ 459.67</def>
            <aliases>
                <symbol comment="DEGREE SIGN">&#xB0;F</symbol>    
                <symbol comment="DEGREE FAHRENHEIT">&#x2109;</symbol>   
                <name> <singular>fahrenheit</singular> </name>
                <name>
                    <singular>degree_fahrenheit</singular>
                    <plural>degrees_fahrenheit</plural>
                </name>
                <name>
                    <singular>degreeF</singular>
                    <plural>degreesF</plural>
                </name>
                <name>
                    <singular>degree_F</singular>
                    <plural>degrees_F</plural>
                </name>
                <name>
                    <singular>degF</singular>
                    <plural>degsF</plural>
                </name>
                <name>
                    <singular>deg_F</singular>
                    <plural>degs_F</plural>
                </name>
            </aliases>
            <definition>unit of thermodynamic temperature</definition>
        </unit>

    <!-- Illumination -->
        <unit>
            <def>1.076391e-1 lx</def>
            <aliases>
                <name> <singular>footcandle</singular> </name>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>3.426259 cd/m^2</def>
            <aliases>
                <name> <singular>footlambert</singular> </name>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>(1e4/pi) cd/m^2</def>
            <aliases>
                <name> <singular>lambert</singular> </name>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e4 cd/m^2</def>
            <aliases>
                <name> <singular>stilb</singular> </name>
                <symbol>sb</symbol>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e4 lm/m^2</def>
            <aliases>
                <name> <singular>phot</singular> </name>
                <symbol>ph</symbol>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1 cd/m^2</def>
            <aliases>
                <name> <singular>nit</singular> </name>
                <symbol>nt</symbol>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>4.184000e4 J/m^2</def>
            <aliases>
                <name> <singular>langley</singular> </name>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>cd/(pi m^2)</def>
            <aliases>
                <name> <singular>blondel</singular> </name>
                <name> <singular>apostilb</singular> </name>
            </aliases>
            <definition>unit of illumination</definition>
        </unit>

    <!-- Miscellaneous -->
        <unit>
            <comment>exact</comment>
            <def>100/m</def>
            <aliases> <name> <singular>kayser</singular> </name> </aliases>
            <definition></definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>gravity</def>
            <aliases>
                <name> <singular>geopotential</singular> </name>
                <name> <singular>dynamic</singular> </name>
                <symbol>gp</symbol>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>2056 hours</def>
            <aliases>
                <name> <singular>work_year</singular> </name>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>work_year/12</def>
            <aliases>
                <name> <singular>work_month</singular> </name>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <comment>exact</comment>
            <def>1e-6 m^2 s^-1 K kg^-1</def>
            <aliases>
                <name> <singular>potential_vorticity_unit</singular> </name>
                <symbol>PVU</symbol>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <def>1</def>
            <aliases>
                <name> <singular>count</singular> </name>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <def>1</def>
            <aliases>
                <name> <singular>bit</singular> </name>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <def>8</def>
            <aliases>
                <name><singular>octet</singular></name>
                <name><singular>byte</singular></name>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <def>446.2 micromoles/meter^2</def>
            <aliases>
                <name> <singular>dobson</singular> </name>
                <symbol>DU</symbol>
            </aliases>
            <definition></definition>
        </unit>
        <unit>
            <def>1/avogadro_constant</def>
            <name><singular>molecule</singular></name>
            <aliases>
                <name><singular>molec</singular></name>
                <name><singular>nucleon</singular></name>
                <name><singular>nuc</singular></name>
            </aliases>
            <definition></definition>
        </unit>
</unit-system>
