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6 Unit definitions

The conversion information is read from a units data file which is called units.dat and is probably located in the /usr/local/share directory. If you invoke units with the -V option, it will print the location of this file. The default file includes definitions for all familiar units, abbreviations and metric prefixes. It also includes many obscure or archaic units.

Many constants of nature are defined, including these:

     pi          ratio of circumference to diameter
     c           speed of light
     e           charge on an electron
     force       acceleration of gravity
     mole        Avogadro's number
     water       pressure per unit height of water
     Hg          pressure per unit height of mercury
     au          astronomical unit
     k           Boltzman's constant
     mu0         permeability of vacuum
     epsilon0    permitivity of vacuum
     G           Gravitational constant
     mach        speed of sound

The database includes atomic masses for all of the elements and numerous other constants. Also included are the densities of various ingredients used in baking so that 2 cups flour_sifted can be converted to grams. This is not an exhaustive list. Consult the units data file to see the complete list, or to see the definitions that are used.

The unit pound is a unit of mass. To get force, multiply by the force conversion unit force or use the shorthand lbf. (Note that g is already taken as the standard abbreviation for the gram.) The unit ounce is also a unit of mass. The fluid ounce is fluidounce or floz. British capacity units that differ from their US counterparts, such as the British Imperial gallon, are prefixed with br. Currency is prefixed with its country name: belgiumfranc, britainpound.

The US Survey foot, yard, and mile can be obtained by using the US prefix. These units differ slightly from the international length units. They were in general use until 1959, and are still used for geographic surveys. The acre is officially defined in terms of the US Survey foot. If you want an acre defined according to the international foot, use intacre. The difference between these units is about 4 parts per million. The British also used a slightly different length measure before 1959. These can be obtained with the prefix UK.

When searching for a unit, if the specified string does not appear exactly as a unit name, then the units program will try to remove a trailing s or a trailing es. If that fails, units will check for a prefix. All of the standard metric prefixes are defined.

To find out what units and prefixes are available, read the standard units data file.