\" $NetBSD: units.1,v 1.23 2019/03/08 08:12:40 msaitoh Exp $
Dd January 6, 2013
Dt UNITS 1
Os
Sh NAME
Nm units
Nd conversion program
Sh SYNOPSIS
Nm
Op Fl Llqv
Op Fl f Ar filename
Oo
Op Ar count
Ar from-unit to-unit
Oc
Sh DESCRIPTION
Nm
converts quantities expression in various scales to
their equivalents in other scales.
Nm
can only handle multiplicative scale changes.
It cannot convert Centigrade to Fahrenheit, for example.
Pp
The following options and arguments are supported:
Bl -tag -width "-fXfilenameX" -offset indent
It Fl f Ar filename
Specifies the name of the units data file to load.
It Fl l No or Fl L
List all unit definitions to the standard output,
instead of performing any conversions.
The result may include error messages and comments, beginning with
Ql \&/ .
Pp
With the
Fl l
option, unit definitions will be listed in a format
almost identical to the units data file that was loaded,
except that comments will be removed, spacing may be changed,
and lines may be re-ordered.
Pp
With the
Fl L
option, all unit definitions will be reduced to a form that
depends on only a few primitive units (such as
Sy m , kg , sec ) .
It Fl q
Suppresses prompting of the user for units and the display of statistics
about the number of units loaded.
It Fl v
Prints the version number.
It Oo Ar count Oc Ar from-unit Ar to-unit
Allows a single unit conversion to be done directly from the command
line.
No prompting will occur.
Nm
will print out only the result of this single conversion.
Specifying
Ar count
and
Ar from-unit
as two separate arguments is equivalent to embedding both parts
inside a single
Ar from-unit
argument, with the parts separated by a space.
El
Pp
Nm
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
Ed
Pp
Powers of units can be specified using the
Dq \&^
character as shown in the example, or by simple concatenation:
Dq cm3
is equivalent to
Dq cm^3 .
Multiplication of units can be specified by using spaces, a dash or
an asterisk.
Division of units is indicated by the slash
Pq Sq \&/ .
Note that multiplication has a higher precedence than division,
so
Dq m/s/s
is the same as
Dq m/s^2
or
Dq "m/s s" .
If the user enters incompatible unit types, the
Nm
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:
Bl -tag -width mercury -compact -offset indent
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
Dq pound
is a unit of mass.
Compound names are run together
so
Dq poundforce
is a unit of force.
British units that differ from their
US counterparts are prefixed with
Dq br ,
and currency is prefixed with
its country name:
Dq belgiumfranc ,
Dq britainpound .
When searching for
a unit, if the specified string does not appear exactly as a unit
name, then the
Nm
program will try to remove a trailing
Dq s
or a trailing
Dq es
and check again for a match.
Pp
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
Sq \&!
characters.
Nm
will not detect infinite loops that could be caused
by careless unit definitions.
Pp
Prefixes are defined in the same way as standard units, but with
a trailing dash at the end of the prefix name.
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 Mt
[email protected]
or
Aq
[email protected]
Sh CAVEATS
While
Nm
can be used as a calculator for many unit-related computations,
caution is required: many computations require additional constant
factors deriving from the physics (or chemistry or whatever) of the
situation.
As these factors are dimensionless,
Nm
cannot itself either provide them or warn the user when they have been
forgotten.
For example, one joule is one kilogram meter squared per second
squared, by definition; however, the kinetic energy of a one-kilogram
object moving at one meter per second is half a joule, not one joule,
because of a dimensionless factor that arises from integration.
Pp
Also, some pairs of units that have the same dimensionality are
nonetheless used to measure different things and attempting to convert
between them may require additional fudge factors or be entirely
meaningless.
For example, torque and energy have the same dimensionality, but
attempting to convert torque in newton-meters to energy in joules is
nonsensical.
There is no practical way for
Nm
to warn about these issues either.
Sh BUGS
The effect of including a
Sq \&/
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
Sq \&|
to indicate division of numbers and
Sq \&/
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 doesn't take so long to load the units list and check
for duplication.
