Units.create :length do |m|
  m.system :english do |s|
    s.unit :name => :inch, :plural => :inches, :abbrev => :in
    s.unit :name => :foot, :plural => :feet, :equals => 12.inches,
      :abbrev => :ft
    s.unit :name => :yard, :equals => 3.feet, :abbrev => :yd
    s.unit :name => :mile, :equals => 5280.feet, :abbrev => :mi
    s.unit :name => :nautical_mile, :equals => 1852.meters, :abbrev => :nmi
    s.format :name => :feet_inches_and_32s,
      :format => lambda { |u|
                          ru = u.round_to_nearest(1.inch,32)
                          feet = ru.feet.floor
                          inches = (ru-feet).inches
                          "#{feet} #{inches.with_fraction 32}" }
  end
  m.system :old_english do |s|
    s.unit :name => :fathom, :equals => 2.yards
    s.unit :name => :chain, :equals => 22.yards
    s.unit :name => :furlong, :equals => 660.feet
    s.unit :name => :league,  :equals => 3.nmi
  end
  m.system :metric do |s|
    s.unit :name => :meter, :equals =>39.37.inches, :abbrev => :m,
      :greek => :ten
    s.unit :name => :anstrom, :equals => 0.1.nanometers, :abbrev => :A
  end
  m.system :astronomical do |s|
    s.unit :name => :astronomical_unit, :equals => 149598000.kilometers,
      :abbrev => :AU
    s.unit :name => :light_year, :equals => speed_of_light*(year.seconds),
      :abbrev => :ly
    s.unit :name => :parsec, :equals => 3.262.light_years, :abbrev => :pc
  end
end