Provided by: units_1.88-1_i386 bug

NAME

       units - unit conversion program

OVERVIEW OF `UNITS'

       The  `units' program converts quantities expressed in various scales to
       their equivalents in other scales.   The  `units'  program  can  handle
       multiplicative  scale  changes as well as nonlinear conversions such as
       Fahrenheit to  Celsius.   Temperature  conversions  require  a  special
       syntax.  See the examples below.

       The  units  are  defined  in  an  external  data file.  You can use the
       extensive data file that comes with this program, or  you  can  provide
       your own data file to suit your needs.

       You  can  use the program interactively with prompts, or you can use it
       from the command line.

INTERACTING WITH `UNITS'

       To invoke units for interactive use, type `units' at your shell prompt.
       The program will print something like this:

           2131 units, 53 prefixes, 24 nonlinear units

           You have:

       At  the  `You  have:'  prompt, type the quantity and units that you are
       converting from.  For example, if you want to  convert  ten  meters  to
       feet,  type  `10  meters'.   Next, `units' will print `You want:'.  You
       should type the type of units you want to convert to.   To  convert  to
       feet,  you  would  type  `feet'.  Note that if the readline library was
       compiled in then the tab key can be used to complete unit  names.   See
       Readline support, for more information about readline.

       The  answer  will  be displayed in two ways.  The first line of output,
       which is marked with a `*' to indicate multiplication, gives the result
       of the conversion you have asked for.  The second line of output, which
       is marked with a `/' to indicate division, gives  the  inverse  of  the
       conversion  factor.   If  you  convert  10 meters to feet, `units' will
       print

               * 32.808399
               / 0.03048

       which tells you that 10 meters equals  about  32.8  feet.   The  second
       number  gives  the conversion in the opposite direction.  In this case,
       it tells you that 1 foot is equal to about 0.03  dekameters  since  the
       dekameter is 10 meters.  It also tells you that 1/32.8 is about .03.

       The  `units'  program prints the inverse because sometimes it is a more
       convenient number.  In the example  above,  for  example,  the  inverse
       value is an exact conversion: a foot is exactly .03048 dekameters.  But
       the number given the other direction is inexact.

       If you try to convert grains to pounds, you will see the following:

           You have: grains
           You want: pounds
                   * 0.00014285714
                   / 7000

       From the second line of the output you can immediately see that a grain
       is equal to a seven thousandth of a pound.  This is not so obvious from
       the first  line  of  the  output.   If  you  find   the  output  format
       confusing, try using the `--verbose' option:

           You have: grain
           You want: aeginamina
                   grain = 0.00010416667 aeginamina
                   grain = (1 / 9600) aeginamina

       If  you  request  a  conversion  between units which measure reciprocal
       dimensions, then `units' will display the conversion  results  with  an
       extra note indicating that reciprocal conversion has been done:

           You have: 6 ohms
           You want: siemens
                   reciprocal conversion
                   * 0.16666667
                   / 6

       Reciprocal conversion can be suppressed by using the `--strict' option.
       As usual, use the `--verbose' option to get more comprehensible output:

           You have: tex
           You want: typp
                   reciprocal conversion
                   1 / tex = 496.05465 typp
                   1 / tex = (1 / 0.0020159069) typp

           You have: 20 mph
           You want: sec/mile
                   reciprocal conversion
                   1 / 20 mph = 180 sec/mile
                   1 / 20 mph = (1 / 0.0055555556) sec/mile

       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:

           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

       If you only want to find the reduced form  or  definition  of  a  unit,
       simply press return at the `You want:' prompt.  Here is an example:

           You have: jansky
           You want:
                   Definition: fluxunit = 1e-26 W/m^2 Hz = 1e-26 kg / s^2

       The  output  from  `units'  indicates  that the jansky is defined to be
       equal to  a  fluxunit  which  in  turn  is  defined  to  be  a  certain
       combination  of  watts,  meters,  and hertz.  The fully reduced (and in
       this case somewhat more cryptic) form appears on the far right.

       Some named units are  treated  as  dimensionless  in  some  situations.
       These include the radian and steradian.  These units will be treated as
       equal to 1 in units  conversions.   Power  is  equal  to  torque  times
       angular  velocity.  This conversion can only be performed if the radian
       is dimensionless.

           You have: (14 ft lbf) (12 radians/sec)
           You want: watts
                   * 227.77742
                   / 0.0043902509

       Note that named dimensionaless units are not treated  as  dimensionless
       in  other  contexts.   They cannot be used as exponents so for example,
       `meter^radian' is not allowed.

       If you want a list of options you can  type  `?'  at  the  `You  want:'
       prompt.   The  program  will  display  a  list of named units which are
       conformable with the unit that you entered at the  `You  have:'  prompt
       above.  Note that conformable unit combinations will not appear on this
       list.

       Typing `help' at either prompt displays a short help message.  You  can
       also  type `help' followed by a unit name.  This will invoke a pager on
       the units data base at the point where that unit is defined.   You  can
       read  the  definition  and  comments  that  may  give  more  details or
       historical information about the unit.

       Typing `search text' will display a list of  all  of  the  units  whose
       names contain `text' as a substring along with their definitions.  This
       may help in the case where you aren't sure of the right unit name.

USING `UNITS' NON-INTERACTIVELY

       The `units' program can  perform  units  conversions  non-interactively
       from the command line.  To do this, type the command, type the original
       units expression, and type the new units you want.  You  will  probably
       need  to protect the units expressions from interpretation by the shell
       using single quote characters.

       If you type

           units '2 liters' 'quarts'

       then `units' will print

               * 2.1133764
               / 0.47317647

       and then exit.  The output tells you that 2 liters is about 2.1 quarts,
       or alternatively that a quart is about 0.47 times 2 liters.

       If  the  conversion is successful, then `units' will return success (0)
       to the calling environment.  If `units' is given non-conformable  units
       to  convert,  it  will  print a message giving the reduced form of each
       unit and it will return failure (nonzero) to the calling environment.

       When `units' is invoked with only one argument, it will print  out  the
       definition  of  the specified unit.  It will return failure if the unit
       is not defined and success if the unit is defined.

UNIT EXPRESSIONS

       In order to enter more complicated units or fractions, you will need to
       use  operations such as powers, products and division.  Powers of units
       can be specified using the `^' character  as  shown  in  the  following
       example, or by simple concatenation: `cm3' is equivalent to `cm^3'.  If
       the exponent is more than one digit, the `^' is required.  An  exponent
       like  `2^3^2'  is  evaluated  right  to left.  The `^' operator has the
       second highest  precedence.   The  `**'  operator  is  provided  as  an
       alternative exponent operator.

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

           You have: arabicfoot * arabictradepound * force
           You want: ft lbf
                   * 0.7296
                   / 1.370614

       Multiplication  of  units  can  be  specified  by  using  spaces, or an
       asterisk (`*').  If `units' is invoked with the `--product' option then
       the  hyphen  (`-') also acts as a multiplication operator.  Division of
       units is indicated by the slash (`/') or by `per'.

           You have: furlongs per fortnight
           You want: m/s
                   * 0.00016630986
                   / 6012.8727

       Historically, multiplication in units was assigned a higher  precedence
       than  division.   This  disagrees with the usual precedence rules which
       give multiplication and division equal precedence, and it  has  been  a
       source of confusion for people who think of units as a calculator.

       By  default,  multiplication  using  the  star  (`*')  now has the same
       precedence as division and hence follows the  usual  precedence  rules.
       If  units  is invoked with the the `--oldstar' option then then the old
       behavior is activated and `*' will have  the  same  precedence  as  the
       other multiplication operators described next.

       Multiplication  using  a  space  or  using  the  hyphen  has  a  higher
       precedence than division and is evaluated left to right.  So  @samp{m/s
       s/day}  is equivalent to `m / s s day' and has dimensions of length per
       time cubed.  Similarly, `1/2 meter' refers  to  a  unit  of  reciprocal
       length  equivalent  to  .5/meter,  which is probably not what you would
       intend if you entered that expression.

       You can indicate division of numbers with the vertical dash  (`|'),  so
       if  you  wanted  half  a  meter you could write @samp{1|2 meter}.  This
       operator has the highest precedence so the square root  of  two  thirds
       could be written `2|3^1|2'.

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

       Parentheses can be used for grouping as desired.

           You have: (1/2) kg / (kg/meter)
           You want: league
                   * 0.00010356166
                   / 9656.0833

       Prefixes  are  defined  separately  from  base  units.  In order to get
       centimeters, the units database defines `centi-' and `c-' as  prefixes.
       Prefixes  can  appear  alone  with no unit following them.  An exponent
       applies only to the immediately preceding unit and its prefix  so  that
       `cm^3' or `centimeter^3' refer to cubic centimeters but `centi*meter^3'
       refers to hundredths of cubic meters.  Only one prefix is permitted per
       unit, so `micromicrofarad' will fail, but `micro*microfarad' will work,
       as will `micro microfarad'..

       For `units', numbers are just another kind of unit.  They can appear as
       many  times  as  you  like  and in any order in a unit expression.  For
       example, to find the volume of a box which is 2 ft by 3 ft by 12 ft  in
       steres, you could do the following:

           You have: 2 ft 3 ft 12 ft
           You want: stere
                   * 2.038813
                   / 0.49048148

           You have: $ 5 / yard
           You want: cents / inch
                   * 13.888889
                   / 0.072

       And  the  second  example  shows  how  the  dollar  sign  in  the units
       conversion can precede the five.  Be careful:  `units'  will  interpret
       `$5' with no space as equivalent to dollars^5.

       Outside  of  the  SI  system,  it  is  often desirable to add values of
       different units together.  You may  also  wish  to  use  `units'  as  a
       calculator  that  keeps  track of units.  Sums of conformable units are
       written with the `+' character.

           You have: 2 hours + 23 minutes + 32 seconds
           You want: seconds
                   * 8612
                   / 0.00011611705

           You have: 12 ft + 3 in
           You want: cm
                   * 373.38
                   / 0.0026782366

           You have: 2 btu + 450 ft lbf
           You want: btu
                   * 2.5782804
                   / 0.38785542

       The expressions which are  added  together  must  reduce  to  identical
       expressions in primitive units, or an error message will be displayed:

           You have: 12 printerspoint + 4 heredium
                                                 ^
           Illegal sum of non-conformable units

       Historically `-' has been used for products of units, which complicates
       its iterpretation in `units'.  Because `units' provides  several  other
       ways to obtain unit products, and because `-' is a subtraction operator
       in general algebraic expressions, `units' treats the binary  `-'  as  a
       subtraction  operator  by  default.  This behavior can be altered using
       the `--product' option which causes `units' to  treat  the  binary  `-'
       operator as a product operator.  Note that when `-' is a multiplication
       operator it has  the  same  precedence  as  `*',  but  when  `-'  is  a
       subtraction  operator  it  has  the  lower  precedence  as the addition
       operator.

       When  `-'  is  used  as  a  unary  operator  it  negates  its  operand.
       Regardless  of  the  `units' options, if `-' appears after `(' or after
       `+' then it will act as a negation operator.  So you can always compute
       20 degrees minus 12 minutes by entering `20 degrees + -12 arcmin'.  You
       must use this construction when you define new units because you cannot
       know what options will be in force when your definition is processed.

       The  `+' character sometimes appears in exponents like `3.43e+8'.  This
       leads to an ambiguity in an expression like `3e+2 yC'.  The unit `e' is
       a  small  unit  of  charge,  so  this  can be regarded as equivalent to
       `(3e+2) yC' or `(3 e)+(2 yC)'.  This ambiguity is  resolved  by  always
       interpreting `+' as part of an exponent if possible.

       Several  built  in  functions  are provided: `sin', `cos', `tan', `ln',
       `log', `log2', `exp', `acos', `atan' and `asin'.  The `sin', `cos', and
       `tan'  functions require either a dimensionless argument or an argument
       with dimensions of angle.

           You have: sin(30 degrees)
           You want:
                   Definition: 0.5

           You have: sin(pi/2)
           You want:
                   Definition: 1

           You have: sin(3 kg)
                             ^
           Unit not dimensionless

       The other functions on the list require dimensionless  arguments.   The
       inverse  trigonometric  functions  return  arguments with dimensions of
       angle.

       If you wish to  take  roots  of  units,  you  may  use  the  `sqrt'  or
       `cuberoot'  functions.   These functions require that the argument have
       the  appropriate  root.   Higher  roots  can   be  obtained  by   using
       fractional exponents:

           You have: sqrt(acre)
           You want: feet
                   * 208.71074
                   / 0.0047913202

           You have: (400 W/m^2 / stefanboltzmann)^(1/4)
           You have:
                   Definition: 289.80882 K

           You have: cuberoot(hectare)
                                     ^
           Unit not a root

       Nonlinear  units  are represented using functional notation.  They make
       possible  nonlinear  unit  conversions  such  temperature.    This   is
       different  from  the linear units that convert temperature differences.
       Note the difference below.  The absolute  temperature  conversions  are
       handled  by  units  starting  with  `temp', and you must use functional
       notation.  The temperature differences are done  using  units  starting
       with `deg' and they do not require functional notation.

           You have: tempF(45)
           You want: tempC
                   7.2222222

           You have: 45 degF
           You want: degC
                   * 25
                   / 0.04

       Think of `tempF(x)' not as a function but as a notation which indicates
       that `x' should have units of `tempF' attached to  it.   See  Nonlinear
       units.   The  first conversion shows that if it's 45 degrees Fahrehneit
       outside it's 7.2 degrees Celsius.   The  second  conversions  indicates
       that  a  change  of 45 degrees Fahrenheit corresponds to a change of 25
       degrees Celsius.

       Some other examples of nonlinears units are ring size and  wire  gauge.
       There  are  numerous  different  gauges  and ring sizes.  See the units
       database for more details.  Note that wire gauges with multiple  zeroes
       are   signified   using  negative  numbers  where  two  zeroes  is  -1.
       Alternatively, you can use the synonyms `g00', `g000', and so  on  that
       are defined in the units database.

           You have: wiregauge(11)
           You want: inches
                   * 0.090742002
                   / 11.020255

           You have: brwiregauge(g00)
           You want: inches
                   * 0.348
                   / 2.8735632

           You have: 1 mm
           You want: wiregauge
                   18.201919

INVOKING `UNITS'

       You invoke `units' like this:

           units [OPTIONS] [FROM-UNIT [TO-UNIT]]

       If  the  FROM-UNIT  and  TO-UNIT are omitted, then the program will use
       interactive prompts to determine which  conversions  to  perform.   See
       Interactive use.  If both FROM-UNIT and TO-UNIT are given, `units' will
       print the result of that single conversion  and  then  exit.   If  only
       FROM-UNIT  appears  on  the  command  line,  `units'  will  display the
       definition of that unit and exit.  Units specified on the command  line
       will need to be quoted to protect them from shell interpretation and to
       group them into two arguments.  See Command line use.

       The following options allow you to read in an alternative  units  file,
       check your units file, or change the output format:

       -c, --check
              Check that all units and prefixes defined in the units data file
              reduce to primitive units.  Print  a  list  of  all  units  that
              cannot  be  reduced.   Also display some other diagnostics about
              suspicious definitions in the units data file.  Note  that  only
              definitions active in the current locale are checked.

       --check-verbose
              Like  the  `-check'  option,  this option prints a list of units
              that cannot be reduced.  But to help find unit  definitions that
              cause endless loops, it lists the units as they are checked.  If
              `units' hangs, then the last  unit  to  be  printed  has  a  bad
              definition.   Note  that  only definitions active in the current
              locale are checked.

       -o format, --output-format format
              Use the specified format for numeric output.  Format is the same
              as  that  for  the  printf function in the ANSI C standard.  For
              example, if you want more precision you might use `-o %.15g'.

       -f filename, --file filename
              Instruct  `units'  to  load  the  units  file  `filename'.    If
              `filename'  is  the empty string (`-f "') then the default units
              file will be loaded.  This enables you to load the default  file
              plus  a  personal  units  file.   Up  to  25  units files may be
              specified on  the  command  line.   This  option  overrides  the
              `UNITSFILE' environment variable.

       -h, --help
              Print out a summary of the options for `units'.

       -m, --minus
              Causes `-' to be interpreted as a subtraction operator.  This is
              usually the default behavior.

       -p, --product
              Causes `-' to be interpreted as a multiplication  operator  when
              it has two operands.  It will act as a negation operator when it
              has only one operand: `(-3)'.   Note  that  by  default  `-'  is
              treated as a subtraction operator.

       ,  --oldstar  Causes  `*' to have the old style precedence, higher than
       the precedence of division so that `1/2*3' will equal `1/6'.

       , --newstar Forces `*' to  have  the  new  (default)  precedence  which
       follows  the  usual rules of algebra: the precedence of `*' is the same
       as the precedence of `/', so that `1/2*3' will equal `3/2'.

       , --compact Give compact output featuring only the  conversion  factor.
       This turns off the `--verbose' option.

       -q, --quiet, --silent
              Suppress  prompting  of  the  user  for units and the display of
              statistics about the number of units loaded.

       -s, --strict
              Suppress conversion of units to  their  reciprocal  units.   For
              example,  `units' will normally convert hertz to seconds because
              these units are reciprocals of each other.   The  strict  option
              requires  that  units  be  strictly  conformable  to  perform  a
              conversion, and will give an error if  you  attempt  to  convert
              hertz to seconds.

       -1, --one-line
              Give  only  one line of output (the forward conversion).  Do not
              print  the  reverse  conversion.   Note  that  if  a  reciprocal
              conversion  is  performed  then  `units'  will  still  print the
              "reciprocal conversion" line.

       -t, --terse
              Give terse output when converting units.   This  option  can  be
              used  when  calling  `units'  from  another  program so that the
              output is easy to parse.  This option has the combined effect of
              these options:  `--strict' `--quiet' `--one-line' `--compact'.

       -v, --verbose
              Give  slightly  more verbose output when converting units.  When
              combined with the `-c' option this  gives  the  same  effect  as
              `--check-verbose'.

       -V, --version
              Print  program version number, tell whether the readline library
              has been included, and give the location of  the  default  units
              data file.

UNIT DEFINITIONS

       The  conversion  information  is  read  from a units data file which is
       called `units.dat' and is probably located  in  the  `/usr/local/share'
       directory.   If  you invoke `units' with the `-V' option, it will print
       the location of this file.  The default file includes  definitions  for
       all  familiar  units,  abbreviations  and  metric  prefixes.   It  also
       includes many obscure or archaic units.

       Many constants of nature are defined, including these:

              pi         ratio of circumference to diameter
              c          speed of light
              e          charge on an electron
              force      acceleration of gravity
              mole       Avogadro's number
              water      pressure per unit height of water
              Hg         pressure per unit height of mercury
              au         astronomical unit
              k          Boltzman's constant

              mu0        permeability of vacuum
              epsilon0   permitivity of vacuum
              G          gravitational constant
              mach       speed of sound
       The database includes  atomic  masses  for  all  of  the  elements  and
       numerous  other  constants.  Also included are the densities of various
       ingredients used in  baking  so  that  `2  cups  flour_sifted'  can  be
       converted  to  `grams'.   This  is not an exhaustive list.  Consult the
       units data file to see the complete list, or  to  see  the  definitions
       that are used.

       The  unit  `pound'  is  a  unit of mass.  To get force, multiply by the
       force conversion unit `force' or use the shorthand `lbf'.   (Note  that
       `g'  is  already taken as the standard abbreviation for the gram.)  The
       unit `ounce' is also a unit of mass.  The fluid ounce  is  `fluidounce'
       or   `floz'.    British  capacity  units  that  differ  from  their  US
       counterparts, such as the British Imperial gallon,  are  prefixed  with
       `br'.   Currency  is  prefixed  with  its country name: `belgiumfranc',
       `britainpound'.

       The US Survey foot, yard, and mile can be obtained by  using  the  `US'
       prefix.   These  units  differ  slightly  from the international length
       units.  They were in general use until 1959, and  are  still  used  for
       geographic  surveys.  The acre is officially defined in terms of the US
       Survey  foot.   If  you  want  an  acre  defined   according   to   the
       international  foot, use `intacre'.  The difference between these units
       is about 4 parts  per  million.   The  British  also  used  a  slightly
       different  length  measure before 1959.  These can be obtained with the
       prefix `UK'.

       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'.  If that fails, `units' will check for
       a prefix.  All of the standard metric prefixes are defined.

       To  find  out  what units and prefixes are available, read the standard
       units data file.

DEFINING NEW UNITS

       All of the units and prefixes that `units' can convert are  defined  in
       the units data file.  If you want to add your own units, you can supply
       your own file.  You can also add your  own  units  definitions  in  the
       `.units.dat'  file  in  your home directory.  If this file exists it is
       read before the units data file.  It will not  be  read  if  any  units
       files are specified on the command line.

       A  unit  is  specified  on  a  single  line  by  giving its name and an
       equivalence.  Comments start with a `#'  character,  which  can  appear
       anywhere   in   a  line.   The  backslash  character  (`ยด)  acts  as  a
       continuation character if it appears as the last character on  a  line,
       making  it  possible  to  spread  definitions out over several lines if
       desired.  A file can be  included  by  giving  the  command  `!include'
       followed  by  the  file's  name.   The  file will be sought in the same
       directory as the parent file unless a full path is given.

       Unit names must not contain any of the operator  characters  `+',  `-',
       `*',  `/', `|', `^' or the parentheses.  They cannot begin with a digit
       or a decimal point (`.'), nor can they end with  a  digit  (except  for
       zero).   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.   Dimensionless  units  are  indicated  by using the string
       `!dimensionless' for the unit definition.

       When adding new units, be sure to use the `-c' option to check that the
       new  units  reduce  properly.   If  you  create  a  loop  in  the units
       definitions, then `units' will hang when invoked with the `-c' options.
       You will need to use the `--check-verbose' option which prints out each
       unit as it checks them.  The program will still hang, but the last unit
       printed will be the unit which caused the infinite loop.

       If  you  define any units which contain `+' characters, carefully check
       them because the `-c' option will not catch non-conformable  sums.   Be
       careful with the `-' operator as well.  When used as a binary operator,
       the `-' character can perform addition or multiplication  depending  on
       the  options used to invoke `units'.  To ensure consistent behavior use
       `-' only as a unary negation operator when writing  units  definitions.
       To  multiply two units leave a space or use the `*' operator with care,
       recalling that it has two possible precedence values  and  may  require
       parentheses  to  ensure consistent behavior.  To compute the difference
       of `foo' and `bar' write `foo+(-bar)' or even `foo+-bar'.

       Here is an example of a short units file that defines some basic units:

              m        !                # The meter is a primitive unit
              sec      !                # The second is a primitive unit
              rad      !dimensionless   # The radian is dimensionless
              micro-   1e-6             # Define a prefix
              minute   60 sec           # A minute is 60 seconds
              hour     60 min           # An hour is 60 minutes
              inch     0.0254 m         # Inch defined in terms of meters
              ft       12 inches        # The foot defined in terms of inches
              mile     5280 ft          # And the mile

                     A unit which ends with a `-' character is a prefix.  If a
                     prefix  definition  contains  any `/' characters, be sure
                     they are protected by parentheses.  If you define  `half-
                     1/2'  then  `halfmeter'  would  be  equivalent  to `1 / 2
                     meter'.

DEFINING NONLINEAR UNITS

       Some  units  conversions  of  interest  are  nonlinear;  for   example,
       temperature  conversions  between  the  Fahrenheit  and  Celsius scales
       cannot be done by simply multiplying by conversions factors.

       When you give a linear unit definition such as `inch 2.54 cm'  you  are
       providing  information  that  `units'  uses to convert values in inches
       into primitive units of  meters.   For  nonlinear  units,  you  give  a
       functional definition that provides the same information.

       Nonlinear  units  are  represented  using a functional notation.  It is
       best to regard this notation not as a function call but  as  a  way  of
       adding  units to a number, much the same way that writing a linear unit
       name after a number adds units to that number.   Internally,  nonlinear
       units  are  defined  by  a  pair of functions which convert to and from
       linear units in the data  file,  so  that  an  eventual  conversion  to
       primitive units is possible.

       Here is an example nonlinear unit definition:

       tempF(x) [1;K] (x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32

       A  nonlinear  unit  definition comprises a unit name, a dummy parameter
       name, two functions, and two corresponding units.  The  functions  tell
       `units'  how  to convert to and from the new unit.  In order to produce
       valid results, the arguments  of  these  functions  need  to  have  the
       correct  dimensions.  To facilitate error checking, you may specify the
       dimensions.

       The definition begins with the unit name followed immediately (with  no
       spaces)  by  a  `('  character.   In  parentheses  is  the  name of the
       parameter.  Next is an optional specification of the units required  by
       the  functions  in  this definition.  In the example above, the `tempF'
       function requires an input argument conformable with `1'.   For  normal
       nonlinear  units  definitions  the  forward function will always take a
       dimensionless  argument.   The  inverse  function  requires  an   input
       argument  conformable  with  `K'.  In general the inverse function will
       need units that match the quantity measured  by  your  nonlinear  unit.
       The  sole  purpose  of  the expression in brackets to enable `units' to
       perform error checking on function arguments.

       Next the function  definitions  appear.   In  the  example  above,  the
       `tempF' function is defined by

           tempF(x) = (x+(-32)) degF + stdtemp

       This  gives  a  rule  for converting `x' in the units `tempF' to linear
       units of absolute temperature, which makes it possible to convert  from
       tempF to other units.

       In  order  to  make conversions to Fahrenheit possible, you must give a
       rule for the inverse conversions. The inverse will  be  `x(tempF)'  and
       its  definition  appears  after  a  `;' character.  In our example, the
       inverse is

           x(tempF) = (tempF+(-stdtemp))/degF + 32

       This inverse definition takes an absolute temperature as  its  argument
       and  converts  it  to  the  Fahrenheit temperature.  The inverse can be
       omitted by leaving out the `;' character, but then conversions  to  the
       unit  will be impossible.  If the inverse is omitted then the `--check'
       option will display a warning.  It is up to you to calculate and  enter
       the  correct  inverse  function  to  obtain  proper  conversions.   The
       `--check' option tests the inverse at one point and print an  error  if
       it is not valid there, but this is not a guarantee that your inverse is
       correct.

       If you wish to make synonyms for nonlinear units,  you  still  need  to
       define  both  the forward and inverse functions.  Inverse functions can
       be obtained using the `~' operator.  So to create a synonym for `tempF'
       you could write

           fahrenheit(x) [1;K] tempF(x); ~tempF(fahrenheit)

       You  may occasionally wish to define a function that operates on units.
       This can be done using a nonlinear unit definition.  For  example,  the
       definition  below  provides conversion between radius and the area of a
       circle.  Note that this definition  requires  a  length  as  input  and
       produces  an  area  as  output,  as  indicated  by the specification in
       brackets.

           circlearea(r) [m;m^2] pi r^2 ; sqrt(circlearea/pi)

       Sometimes you may be interested in a piecewise linear unit such as many
       wire  gauges.   Piecewise  linear  units  can  be defined by specifying
       conversions to linear units on a list of points.  Conversion  at  other
       points  will  be done by linear interpolation.  A partial definition of
       zinc gauge is

           zincgauge[in] 1 0.002, 10 0.02, 15 0.04, 19 0.06, 23 0.1

       In this example, `zincgauge' is the name of the piecewise linear  unit.
       The  definition  of  such  a  unit  is  indicated  by  the embedded `['
       character.  After the bracket, you should  indicate  the  units  to  be
       attached  to the numbers in the table.  No spaces can appear before the
       `]' character, so  a  definition  like  `foo[kg  meters]'  is  illegal;
       instead write `foo[kg*meters]'.  The definition of the unit consists of
       a list of pairs optionally separated by commas.  This  list  defines  a
       function for converting from the piecewise linear unit to linear units.
       The first item in each pair is the function argument; the  second  item
       is  the  value of the function at that argument (in the units specified
       in brackets).  In this example, we define `zincgauge' at  five  points.
       For  example,  we  set `zincgauge(1)' equal to `0.002 in'.  Definitions
       like this  may  be   more  readable   if  written  using   continuation
       characters as
              zincgauge[in]         \
                      1        0.002 \
                      10        0.02 \
                      15        0.04 \
                      19        0.06 \
                      23        0.1

       With  the  preceeding  definition,  the  following  conversion  can  be
       performed:

           You have: zincgauge(10)
           You want: in
               * 0.02
               / 50
           You have: .01 inch
           You want: zincgauge
               5

       If you define a piecewise linear unit that is not  strictly  monotonic,
       then the inverse will not be well defined.  If the inverse is requested
       for such a  unit,  `units'  will  return  the  smallest  inverse.   The
       `--check'  option  will  print  a  warning if a non-monotonic piecewise
       linear unit is encountered.

LOCALIZATION

       Some  units  have  different  values  in  different   locations.    The
       localization feature accomodates this by allowing the units database to
       specify region dependent definitions.   A locale region  in  the  units
       database begins with `!locale' followed by the name of the locale.  The
       leading `!' must appear in the first column of the units database.  The
       locale  region  is  terminated  by `!endlocale'.  The following example
       shows how to define a couple units in a locale.

       !locale en_GB
       ton                     brton
       gallon                  brgallon
       !endlocale

       The current locale is specified by the `LOCALE'  environment  variable.
       Note  that the `-c' option only checks the definitions which are active
       for the current locale.

ENVIRONMENT VARIABLES

       The `units' programs uses the following environment variables.

       LOCALE Specifies the locale.  The default is `en_US'.  Sections of  the
              units database are specific to certain locales.

       PAGER  Specifies  the  pager  to  use  for  help and for displaying the
              conformable units.  The help function browses the units database
              and calls the pager using the `+nn' syntax for specifying a line
              number.  The default pager is `more', but  `less',  `emacs',  or
              `vi' are possible alternatives.

       UNITSFILE
              Specifies  the  units  database  file  to  use  (instead  of the
              default). This will be overridden by the `-f' option.  Note that
              you  can  only  specify  a  single  units  database  using  this
              environment variable.

READLINE SUPPORT

       If the `readline' package has been compiled in, then  when  `units'  is
       used   interactively,   numerous  command  line  editing  features  are
       available.  To check if your version of `units' includes the  readline,
       invoke the program with the `--version' option.

       For  complete information about readline, consult the documentation for
       the readline package.  Without any configuration,  `units'  will  allow
       editing  in the style of emacs.  Of particular use with `units' are the
       completion commands.

       If you type a few characters and then hit `ESC' followed by the `?' key
       then  `units' will display a list of all the units which start with the
       characters typed.  For example, if you type  `metr'  and  then  request
       completion, you will see something like this:

       You have: metr
       metre             metriccup         metrichorsepower  metrictenth
       metretes          metricfifth       metricounce       metricton
       metriccarat       metricgrain       metricquart       metricyarncount
       You have: metr

       If  there  is  a unique way to complete a unitname, you can hit the tab
       key and `units' will provide the rest of the  unit  name.   If  `units'
       beeps,  it  means that there is no unique completion.  Pressing the tab
       key a second time will print the list of all completions.

FILES

       /usr/share/misc/units.dat - the standard units data file

AUTHOR

       Adrian Mariano (adrian@cam.cornell.edu)

                                  25 Sep 2007                         UNITS(1)