UNITS(1)

NAME
units - conversion program

SYNOPSIS
units [-qv] [-f filename] [from-unit to-unit]

DESCRIPTION
The units program converts quantities expressed in various scales to their equivalents in other scales. The units program can only handle multiplicative scale changes. It cannot convert Celsius to Fahrenheit, for example. It also does not handle logarithmic units such as bels.

units works interactively by prompting the user for input:

    You have: meters
    You want: feet
            * 3.2808399
            / 0.3048
    You have: cm^3
    You want: gallons
            * 0.00026417205
            / 3785.4118

That is, one meter equals roughly 3.28 feet (or, conversely, one foot is roughly equal to 0.3 meters), and one gallon is roughly equal to 3785 cubic cm.

The units program can handle numbers as well:

    You have: 60 miles/hr
    You want: km/hr
            * 96.56064
            / 0.010356187
    You have: 100 USD
    You want: 10 euro
            * 7.4354971
            / 0.13449

In other words, 60 miles per hour is about 96.6 km/hr, and 100 US dollars will get you seven 10-Euro notes.

The options are as follows:

-f filename
    Specifies the name of the units data file to load.

-q  Suppresses prompting of the user for units and the display of statistics about the number of units loaded.

-v  Prints the version number.

from-unit to-unit
    Allows a single unit conversion to be done directly from the command line. No prompting will occur. The units program will print out only the result of this single conversion.

Powers of units can be specified using the ‘^’ character as shown in the example, or by simple concatenation: ‘cm3’ is equivalent to ‘cm^3’. Multiplication of units can be specified by using spaces, a dash or an asterisk. Division of units is indicated by the slash (‘/’). Note that multiplication has a higher precedence than division, so ‘m/s/s’ is the same as ‘m/s^2’ or ‘m/s s’. If the user enters incompatible unit types, the units program will print a message indicating that the units are not conformable and it will display the reduced form for each unit:

    You have: ergs/hour
    You want: fathoms kg^2 / day
    conformability error
            2.7777778e-11 kg m^2 / sec^3
            2.1166667e-05 kg^2 m / sec

The conversion information is read from a units data file. The default file includes definitions for most familiar units, abbreviations and metric prefixes. Some constants of nature included are:

pi  ratio of circumference to diameter
c   speed of light
e   charge on an electron
g   acceleration of gravity
force
    same as g
mole
    Avogadro's number
water
    pressure per unit height of water (at 4 C)
mercury
    pressure per unit height of mercury
ao  Bohr radius
AU  astronomical unit

‘Pound’ is a unit of mass. Compound names are run together so ‘poundforce’ is a unit of force. British units that differ from their US counterparts are prefixed with ‘br’, and currency is prefixed with its country name: ‘belgiumfranc’, ‘britainpound’. 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’ and check again for a match.

All of these definitions can be read in the standard units file, or you can supply your own file. A unit is specified on a single line by giving its name and an equivalence. One should be careful to define new units in terms of old ones so that a reduction leads to the primitive units which are marked with ‘’! characters. The units program will not detect infinite loops that could be caused by careless unit definitions.

Prefixes are defined in the same way as standard units, but with a trailing dash at the end of the prefix name. Prefixes are applied after the longest matching unit name is found; for example, “nmile” is taken to be a nautical mile rather than a nanomile.

FILES

/usr/share/misc/units.lib
    the standard units library

SEE ALSO
International Bureau of Weights and Measures, The International System of Units, http://www.bipm.org/utils/common/pdf/si_brochure_8.pdf. ISO 4217, Codes for the representation of currencies and funds, 2008. ISO/IEC 80000, Quantities and units — Part 13: Information science and technology.

AUTHORS
Adrian Mariano (adrian@cam.cornell.edu or mariano@geom.umn.edu)

BUGS
The effect of including a ‘/’ in a prefix is surprising.

Exponents of units entered by the user can be only one digit. You can work around this by multiplying several terms.

The user must use ‘|’ to indicate division of numbers and ‘/’ to indicate division of symbols. This distinction should not be necessary.

Prefixes specified without a unit are treated as dimensionless quantities. This can lead to confusion when some prefixes are also defined as units (e.g., m). For example, Tera- / Giga- is 1000, but one Tesla (T) is 10,000 Gauss (G).

Some non-SI units have multiple definitions (e.g., barrel, calorie) and others have changed over time (e.g., cubit). In particular, monetary values fluctuate.

The program contains various arbitrary limits on the length of the units converted and on the length of the data file.

The program should use a hash table to store units so that it doesn't take so long to load the units list and check for duplication.