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14 July 1993 UNITS(1)
NAME
units - conversion program
SYNTAX
units [-f filename] [-q] [to-unit from-unit]
SUMMARY
-f filename
Specifies the name of the units data file to load.
-q Supresses prompting of the user for units and the display of statis-
tics about the number of units loaded.
from-unit to-unit
Allows a single unit converstion to be done directly from the com-
mand line. No prompting will occur. The units program will print
out only the result of this single conversion.
DESCRIPTION
The units program converts quantities expression in various scales to
their equivalents in other scales. The units program can only handle
multiplicative scale changes. It cannot convert Centigrade to
Fahrenheit, for example. It 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
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 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
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UNITS(1) 14 July 1993
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
mercury pressure per unit height of mercury
au astronomical unit
'Pound' is a unit of mass. Compound names are run together so 'pound-
force' 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 giv-
ing 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 was as standard units, but with a
trailing dash at the end of the prefix name.
BUGS
The effect of including a '/' in a prefix is surprising.
Exponents entered by the user can be only one digit.
The user must use | to indicate division of numbers and / to indicate
division of symbols. This distinction should not be necessary.
The program contains various arbitrary limits on the length of the units
converted and on the length of the data file.
FILES
units.lib - the standard units library
AUTHOR
Adrian Mariano (adrian@u.washington.edu or mariano@geom.umn.edu)
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