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.TH UNITS 1
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.if n .ds / /
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.SH NAME
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units \- conversion program
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.SH SYNOPSIS
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.B units
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[
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.B -v
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]
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[
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.I file
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]
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.SH DESCRIPTION
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.I Units
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converts quantities expressed
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in various standard scales to
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their equivalents in other scales.
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It works interactively in this fashion:
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.IP
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.EX
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you have: inch
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you want: cm
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    * 2.54
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    / 0.393701
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.EE
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.PP
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A quantity is specified as a multiplicative combination
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of units and floating point numbers.
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Operators have the following precedence:
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.IP
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.EX
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.ta \w'\fLXXXXXXXXXXXXXXX'u
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\fL+\fP \fL-\fP	\f1add and subtract
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\fL*\fP \fL/\fP \fL×\fP \fL÷\fP	\f1multiply and divide
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catenation	multiply
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\fL²\fP \fL³\fP \fL^\fP	\f1exponentiation
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\fL|\fP	\f1divide
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\fL(\fP ... \fL)\fP	\f1grouping
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.EE
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.PP
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Most familiar units,
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abbreviations, and metric prefixes are recognized,
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together with a generous leavening of exotica
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and a few constants of nature including:
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.IP
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.de fq
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\fL\\$1\\fP	\\$2 \\$3 \\$4 \\$5 \\$6
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..
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.ta \w'\fLwaterXXX'u
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.nf
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.fq pi,\f1π\fP ratio of circumference to diameter
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.fq c speed of light
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.fq e charge on an electron
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.fq g acceleration of gravity
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.fq force same as \fLg\fP
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.fq mole Avogadro's number
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.fq water "pressure head per unit height of water"
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.fq au astronomical unit
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.fi
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.PP
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The
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.L pound
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is a unit of
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mass.
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Compound names are run together, e.g.
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.LR lightyear .
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British units that differ from their US counterparts
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are prefixed thus:
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.LR brgallon .
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Currency is denoted
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.LR belgiumfranc ,
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.LR britainpound ,
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etc.
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.PP
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The complete list of units can be found in
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.BR /lib/units .
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A
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.I file
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argument to
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.I units
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specifies a file to be used instead of
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.BR /lib/units.
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The
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.B -v
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flag causes
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.I units
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to print its entire database.
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.SH EXAMPLE
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.EX
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you have: 15 pounds force/in²
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you want: atm
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    * 1.02069
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    / .97973
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.EE
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.SH FILES
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.B /lib/units
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.SH SOURCE
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.B /sys/src/cmd/units.y
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.SH BUGS
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Since
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.I units
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does only multiplicative scale changes,
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it can convert Kelvin to Rankine but not Centigrade to
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Fahrenheit.
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.PP
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Currency conversions are only as accurate as the last time someone
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updated the database.