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.\" $FreeBSD: release/9.1.0/usr.bin/units/units.1 225596 2011-09-15 19:52:43Z dwmalone $
.Dd July 14, 1993
.Dt UNITS 1
.Os
.Sh NAME
.Nm units
.Nd conversion program
.Sh SYNOPSIS
.Nm
.Op Fl f Ar filename
.Op Fl qv
.Op Ar from-unit to-unit
.Sh OPTIONS
The following options are available:
.Bl -tag -width indent
.It Fl f Ar filename
Specify the name of the units data file to load.
.It Fl q
Suppress prompting of the user for units and the display of statistics
about the number of units loaded.
.It Fl v
Print the version number.
.It Ar from-unit to-unit
Allow a single unit conversion to be done directly from the command
line.
The program will not print prompts.
It will print out the
result of the single specified conversion.
.El
.Sh DESCRIPTION
The
.Nm
program converts quantities expressed in various scales to
their equivalents in other scales.
The
.Nm
program can only
handle multiplicative or affine scale changes.
It works interactively by prompting
the user for input:
.Bd -literal
    You have: meters
    You want: feet
            * 3.2808399
            / 0.3048

    You have: cm^3
    You want: gallons
            * 0.00026417205
            / 3785.4118

    You have: meters/s
    You want: furlongs/fortnight
            * 6012.8848
            / 0.00016630952

    You have: 1|2 inch
    You want: cm
            * 1.27
            / 0.78740157

    You have: 85 degF
    You want: degC
	29.444444
.Ed
.Pp
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'.
Division of numbers
must be indicated using the vertical bar ('|').
To convert half a
meter, you would write '1|2 meter'.
If you write '1/2 meter' then the
units program would interpret that as equivalent to '0.5/meter'.
If you enter 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:
.Bd -literal
    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
.Ed
.Pp
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:
.Pp
.Bl -column -offset indent -compact "mercury"
.It "pi	ratio of circumference to diameter
.It "c	speed of light
.It "e	charge on an electron
.It "g	acceleration of gravity
.It "force	same as g
.It "mole	Avogadro's number
.It "water	pressure per unit height of water
.It "mercury	pressure per unit height of mercury
.It "au	astronomical unit
.El
.Pp
The unit 'pound' is a unit of mass.
Compound names are run together
so 'pound force' is a unit of force.
The unit 'ounce' is also a unit
of mass.
The fluid ounce is 'floz'.
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
.Nm
will try to remove a trailing 's' or a
trailing 'es' and check again for a match.
.Pp
To find out what units are available read the standard units file.
If you want to add your own units you can supply your own file.
A unit is specified on a single line by
giving its name and an equivalence.
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
.Nm
program will not detect infinite loops that could be caused
by careless unit definitions.
Comments in the unit definition file
begin with a '/' character at the beginning of a line.
.Pp
Prefixes are defined in the same was as standard units, but with
a trailing dash at the end of the prefix name.
If a unit is not found
even after removing trailing 's' or 'es', then it will be checked
against the list of prefixes.
Prefixes will be removed until a legal
base unit is identified.
.Pp
Here is an example of a short units file that defines some basic
units.
.Pp
.Bl -column -offset indent -compact "minute"
.It "m	!a!
.It "sec	!b!
.It "micro-	1e-6
.It "minute	60 sec
.It "hour	60 min
.It "inch	0.0254 m
.It "ft	12 inches
.It "mile	5280 ft
.El
.Sh FILES
.Bl -tag -width /usr/share/misc/units.lib -compact
.It Pa /usr/share/misc/units.lib
the standard units library
.El
.Sh AUTHORS
.An Adrian Mariano Aq adrian@cam.cornell.edu
.Sh BUGS
The effect of including a '/' in a prefix is surprising.
.Pp
Exponents entered by the user can be only one digit.
You can work around this by multiplying several terms.
.Pp
The user must use | to indicate division of numbers and / to
indicate division of symbols.
This distinction should not
be necessary.
.Pp
The program contains various arbitrary limits on the length
of the units converted and on the length of the data file.
.Pp
The program should use a hash table to store units so that
it does not take so long to load the units list and check
for duplication.