NAME

    Convert::Units::Base - base object for performing unit
    conversions

DESCRIPTION

    The Units package is a collection of modules for parsing strings
    with unit measurements (such as "12pt" or "3 meters") and
    converting them to some other unit (such as "picas" or
    "inches").

    It uses a base package (Units::Base) which does the dirty work.
    Other modules define what units they handle and how they are
    related.

  Why a Separate Module?

    It is *intentionally* distinct from the *Math::Units* module.
    Why? The *Math::Units* module implies that unit conversions are
    *exact*, with one-to-one relationships. This is fine for
    scientific work. It's even fine for some general purpose/real-
    world uses (such as converting Fehrenheight to Celcius).

    Real-world measurement systems are conflicting. For instance, a
    "point" in typography is equivalent to 1/72 inch, according to
    PostScript specs and common usage. Other type systems consider
    it 1/72.27 inch, or 0.01383 inches, or 0.0148 inches. Outside of
    that context, a point may be 1/120 or 1/144 inch.

    Common notations and abbreviations also depend on context. Does
    "12 pt" mean "12 point", "12 parts" or "12 pints"?

    Even without conflicts in the definition of a particular unit,
    there's no need to convert point sizes for fonts into miles or
    light-years. Typesetters, surveyors and astronomers user
    different scales as well as systems.

  People do not think like computers

    Not everyone uses the metric system.

    And even less people say things like "5.25 feet". Often it's "5
    feet, 3 inches" or "5 1/4 feet".

    Despite having ten fingers and toes, people don't think in tens.
    They think in twos, threes, fours, twelves, and sixteens. And
    sometimes they use fractional measurements like quarter-inches,
    sixteenths-of-an-inch, or half-pints.

    The purpose of this module is to allow people to use the
    measurement systems they are familiar with, and that is
    appropriate to what they are doing.

  Rationale

    The Units:: hierarchy is an attempt to keep measurement systems
    in distinct classes. Thus one can have modules for converting
    between typography units (points, picas) distinct from common
    units of length (or area, temperature, etc.), specialized units
    (for Astronomy, Chemistry, Physics, Textiles, Winery,
    Navigation, etc.) or even traditional or regional systems
    (Japanese, Chinese, Egyptian, archaic systems, etc.) and to keep
    conflicting measurement systems distinct.

  Release Notes

    The current distribution contains the following packages:

        Convert::Units::
        ::Base         - a base module that does all of the work
        ::Length       - a module for converting units of length
        ::Temperature  - a module for converting units of temperature
        ::Type         - a module for converting units of type

    Units::Base by itself does nothing. Another module needs to use
    it to create definitions of what units of measurement it handles
    and how they are related to each other (ie, 1 m = 100 cm).

    The base unit also allows for synonym and abbreviations to be
    defined.

    It also allows common "multiples" to be defined, so that it can
    handle things like "18 half-points" or "6 dozen feet" or even
    convert millimters to "sixteenths of an inch". (It does not yet
    handle Greek prefixes like centi- or mega- ... those will have
    to be manually defined.)

  Known Issues

    The current release should be considered "beta" until further
    testing and refinements have been made. Then again, maybe
    "alpha" is more accurate.

    The current version does not yet handle fractions such as "1/2
    in". It should handle decimals such as "0.5 in".

    Relationships have been rewritten to be handle A(x+b) as well
    Ax. They may be redone in the future to handle more complex
    relationships, if the need arises.

    Unit names much be defined as all lowercase, since strings are
    munged with *lc()* before processing. In other words, if you
    define a unit name as "F" or "Fahrenheight" you won't be able to
    use it.

  Future Enhancements

    Aside from bug fixes, optimizations, and making the string
    parsing conform more to the "manifesto" above, obvious additions
    would be modules for converting between units of area, volume,
    weight... (although if *Math::Units* does what you need, use
    that instead.)

    An example hierarchy for future modules:

        Convert::Units::
        ::Length            - general measures of length
        ::Area
        ::Pressure
        ::Volume

        Convert::Units::Length
        ::Chinese           - specialized regional/traditional systems
        ::English

        Convert::Units::Astronomy
        ::Length            - or Distance...?

    Modules should share a common unit (preferably metric) to allow
    for conversions.

REQUIRED MODULES

        Carp

SEE ALSO

    *Units::Length*, *Units::Temperature* and *Units::Type* modules,
    which demonstrate how *Units::Base* is used.

AUTHOR

    Robert Rothenberg <wlkngowl@unix.asb.com>

LICENSE

    Copyright (c) 1999 Robert Rothenberg. All rights reserved. This
    program is free software; you can redistribute it and/or modify
    it under the same terms as Perl itself.

