=Ruby Units

Version: 0.3.6

Kevin C. Olbrich, Ph.D. 
kevin.olbrich@gmail.com

http://www.sciwerks.com

Project page: http://rubyforge.org/projects/ruby-units

==Introduction
Many technical applications make use of specialized calculations at some point.  Frequently, these calculations require unit conversions to ensure accurate results.  Needless to say, this is a pain to properly keep track of, and is prone to numerous errors.
  
==Solution
The 'Ruby units' gem is designed so simplify the handling of units for scientific calculations.  The units of each quantity are specified when a Unit object is created and the Unit class will handle all subsequent conversions and manipulations to ensure an accurate result.
  
==Installation:
This package may be installed using:
 gem install ruby-units
  
==Usage:
 unit = Unit.new("1")             # constant only
 unit = Unit.new("mm")            # unit only (defaults to a value of 1)
 unit = Unit.new("1 mm")          # create a simple unit
 unit = Unit.new("1 mm/s")        # a compound unit
 unit = Unit.new("1 mm s^-1")     # in exponent notation
 unit = Unit.new("1 kg*m^2/s^2")  # complex unit
 unit = Unit.new("1 kg m^2 s^-2") # complex unit
 unit = Unit("1 mm")              # shorthand
 unit = "1 mm".to_unit            # convert string object
 unit = object.to_unit            # convert any object using object.to_s
 unit = U'1 mm'
 unit = u'1 mm'
 unit = '1 mm'.unit
 unit = '1 mm'.u
 

==Rules:  
1. only 1 quantity per unit (with 2 exceptions... 6'5" and '8 lbs 8 oz')
2. use SI notation when possible
3. avoid using spaces in unit names

==Unit compatability:
Many methods require that the units of two operands are compatible.  Compatible units are those that can be easily converted into each other, such as 'meters' and 'feet'.

 unit1 =~ unit2   #=> true if units are compatible

==Unit Math:

<b>Method</b>::  <b>Comment</b>
 Unit#+()::       Add. only works if units are compatible
 Unit#-()::       Subtract. only works if units are compatible
 Unit#*()::       Multiply.  
 Unit#/()::       Divide.
 Unit#**()::      Exponentiate.  Exponent must be an integer, can be positive,  negative, or zero                        
 Unit#inverse:: Returns 1/unit
 Unit#abs::     Returns absolute value of the unit quantity.  Strips off the  units
 Unit#ceil::    rounds quantity to next highest integer
 Unit#floor::   rounds quantity down to next lower integer
 Unit#round::   rounds quantity to nearest integer
 Unit#to_int::  returns the quantity as an integer
 
Unit will coerce other objects into a Unit if used in a formula.  This means that ..
 
 Unit("1 mm") + "2 mm"  == Unit("3 mm")
 
This will work as expected so long as you start the formula with a Unit object. 

==Conversions & comparisons

Units can be converted to other units in a couple of ways.

 unit1 = unit >> "ft"   # => convert to 'feet'
 unit >>= "ft"          # => convert and overwrite original object
 unit3 = unit1 + unit2  # => resulting object will have the units of unit1
 unit3 = unit1 - unit2  # => resulting object will have the units of unit1
 unit1 <=> unit2        # => does comparison on quantities in base units, 
                          throws an exception if not compatible
 unit1 === unit2        # => true if units and quantity are the same, even if
                          'equivalent' by <=>
 unit.to('ft')          # convert
 unit1 + unit2 >> "ft"  # converts result of math to 'ft'
 (unit1 + unit2).to('ft') # converts result to 'ft'
 
==Text Output
Units will display themselves nicely based on the preferred abbreviation for the units and prefixes.
Since Unit implements a Unit#to_s, all that is needed in most cases is:
 "#{Unit.new('1 mm')}"  #=> "1 mm"
 
The to_s also accepts some options.
 Unit.new('1.5 mm').to_s("%0.2f")  # => "1.50 mm".  Enter any valid format
                                      string.  Also accepts strftime format
 U('1.5 mm').to_s("in")     # => converts to inches before printing
 U("2 m").to_s(:ft)         #=> returns 6'7"
 U("100 kg").to_s(:lbs)     #=> returns 220 lbs, 7 oz
 
 
==Time Helpers

Time, Date, and DateTime objects can have time units added or subtracted.

Time.now + "10 min".unit 

Several helpers have also been defined.
Note: If you include the 'Chronic' gem, you can specify times in natural
      language.

'min'.since('9/18/06 3:00pm')
'min'.before('9/18/08 3:00pm')
'days'.until('1/1/07')
'5 min'.from(Time.now)
'5 min'.from_now
'5 min'.before_now
'5 min'.before(Time.now)
'10 min'.ago

==Ranges

[U('0 h')..U('10 h')].each {|x| p x}
works so long as the starting point has an integer scalar

==Math functions
All Trig math functions (sin, cos, sinh, ...) can take a unit as their parameter.  It will be converted to radians and then used if possible.