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) 1999-2000 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.