230 lines
6 KiB
Groff
230 lines
6 KiB
Groff
.\" $NetBSD: units.1,v 1.21 2013/07/20 21:40:01 wiz Exp $
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.Dd January 6, 2013
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.Dt UNITS 1
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.Os
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.Sh NAME
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.Nm units
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.Nd conversion program
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.Sh SYNOPSIS
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.Nm
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.Op Fl Llqv
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.Op Fl f Ar filename
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.Oo
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.Op Ar count
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.Ar from-unit to-unit
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.Oc
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.Sh DESCRIPTION
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.Nm
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converts quantities expression in various scales to
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their equivalents in other scales.
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.Nm
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can only handle multiplicative scale changes.
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It cannot convert Centigrade to Fahrenheit, for example.
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.Pp
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The following options and arguments are supported:
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.Bl -tag -width "-fXfilenameX" -offset indent
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.It Fl f Ar filename
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Specifies the name of the units data file to load.
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.It Fl l No or Fl L
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List all unit definitions to the standard output,
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instead of performing any conversions.
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The result may include error messages and comments, beginning with
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.Ql \&/ .
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.Pp
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With the
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.Fl l
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option, unit definitions will be listed in a format
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almost identical to the the units data file that was loaded,
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except that comments will be removed, spacing may be changed,
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and lines may be re-ordered.
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.Pp
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With the
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.Fl L
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option, all unit definitions will be reduced to a form that
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depends on only a few primitive units (such as
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.Sy m , kg , sec ) .
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.It Fl q
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Suppresses prompting of the user for units and the display of statistics
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about the number of units loaded.
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.It Fl v
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Prints the version number.
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.It Oo Ar count Oc Ar from-unit Ar to-unit
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Allows a single unit conversion to be done directly from the command
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line.
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No prompting will occur.
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.Nm
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will print out only the result of this single conversion.
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Specifying
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.Ar count
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and
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.Ar from-unit
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as two separate arguments is equivalent to embedding both parts
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inside a single
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.Ar from-unit
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argument, with the parts separated by a space.
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.El
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.Pp
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.Nm
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works interactively by prompting the user for input:
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.Bd -literal
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You have: meters
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You want: feet
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* 3.2808399
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/ 0.3048
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You have: cm^3
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You want: gallons
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* 0.00026417205
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/ 3785.4118
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.Ed
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.Pp
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Powers of units can be specified using the
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.Dq \&^
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character as shown in the example, or by simple concatenation:
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.Dq cm3
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is equivalent to
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.Dq cm^3 .
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Multiplication of units can be specified by using spaces, a dash or
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an asterisk.
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Division of units is indicated by the slash
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.Pq Sq \&/ .
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Note that multiplication has a higher precedence than division,
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so
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.Dq m/s/s
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is the same as
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.Dq m/s^2
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or
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.Dq "m/s s" .
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If the user enters incompatible unit types, the
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.Nm
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program will print a message indicating that the units are not
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conformable and it will display the reduced form for each unit:
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.Bd -literal
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You have: ergs/hour
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You want: fathoms kg^2 / day
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conformability error
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2.7777778e-11 kg m^2 / sec^3
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2.1166667e-05 kg^2 m / sec
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.Ed
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.Pp
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The conversion information is read from a units data file.
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The default
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file includes definitions for most familiar units, abbreviations and
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metric prefixes.
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Some constants of nature included are:
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.Bl -tag -width mercury -compact -offset indent
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.It pi
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ratio of circumference to diameter
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.It c
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speed of light
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.It e
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charge on an electron
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.It g
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acceleration of gravity
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.It force
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same as g
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.It mole
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Avogadro's number
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.It water
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pressure per unit height of water
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.It mercury
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pressure per unit height of mercury
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.It au
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astronomical unit
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.El
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.Pp
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.Dq pound
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is a unit of mass.
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Compound names are run together
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so
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.Dq poundforce
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is a unit of force.
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British units that differ from their
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US counterparts are prefixed with
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.Dq br ,
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and currency is prefixed with
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its country name:
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.Dq belgiumfranc ,
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.Dq britainpound .
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When searching for
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a unit, if the specified string does not appear exactly as a unit
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name, then the
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.Nm
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program will try to remove a trailing
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.Dq s
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or a trailing
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.Dq es
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and check again for a match.
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.Pp
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All of these definitions can be read in the standard units file, or you
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can supply your own file.
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A unit is specified on a single line by
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giving its name and an equivalence.
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One should be careful to define
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new units in terms of old ones so that a reduction leads to the
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primitive units which are marked with
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.Sq \&!
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characters.
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.Nm
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will not detect infinite loops that could be caused
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by careless unit definitions.
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.Pp
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Prefixes are defined in the same way as standard units, but with
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a trailing dash at the end of the prefix name.
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.Sh FILES
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.Bl -tag -width /usr/share/misc/units.lib -compact
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.It Pa /usr/share/misc/units.lib
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the standard units library
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.El
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.Sh AUTHORS
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.An Adrian Mariano Aq Mt adrian@cam.cornell.edu
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or
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.Aq mariano@geom.umn.edu
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.Sh CAVEATS
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While
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.Nm
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can be used as a calculator for many unit-related computations,
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caution is required: many computations require additional constant
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factors deriving from the physics (or chemistry or whatever) of the
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situation.
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As these factors are dimensionless,
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.Nm
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cannot itself either provide them or warn the user when they have been
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forgotten.
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For example, one joule is one kilogram meter squared per second
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squared, by definition; however, the kinetic energy of a one-kilogram
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object moving at one meter per second is half a joule, not one joule,
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because of a dimensionless factor that arises from integration.
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.Pp
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Also, some pairs of units that have the same dimensionality are
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nonetheless used to measure different things and attempting to convert
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between them may require additional fudge factors or be entirely
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meaningless.
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For example, torque and energy have the same dimensionality, but
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attempting to convert torque in newton-meters to energy in joules is
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nonsensical.
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There is no practical way for
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.Nm
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to warn about these issues either.
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.Sh BUGS
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The effect of including a
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.Sq \&/
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in a prefix is surprising.
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.Pp
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Exponents entered by the user can be only one digit.
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You can work around this by multiplying several terms.
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.Pp
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The user must use
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.Sq \&|
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to indicate division of numbers and
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.Sq \&/
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to indicate division of symbols.
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This distinction should not be necessary.
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.Pp
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The program contains various arbitrary limits on the length
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of the units converted and on the length of the data file.
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.Pp
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The program should use a hash table to store units so that
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it doesn't take so long to load the units list and check
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for duplication.
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