Units.create :mass do |m|
  m.system :metric do |s|
    s.unit :name => :gram, :abbrev => :g, :greek => :ten
  end
end

Units.create :weight do |m|
  m.system :avoirdupois do |s|
    s.unit :name => :grain, :equals => (1/7000.0).lb, :abbrev => :gr
    s.unit :name => :dram, :equals => (1/16.0).oz, :abbrev => :dr
    s.unit :name => :ounce, :equals => (1/16.0).lb, :abbrev => :oz
    s.unit :name => :pound, :equals => 454.g, :abbrev => :lb
    s.unit :name => :hundredweight, :equals => 100.lb, :abbrev => :cwt
    s.unit :name => :ton, :equals => 20.cwt
  end
end