gistfile1.txt

  Units = { :dollar_per_ffe => { :symbol => "$/ffe", :si_factor=>1.0 },
            :dollar_per_ton => { :symbol => "$/T", :si_factor=>1.0e-3 }
          }

  Attribute_Units = { :default_transshipment_cost => :dollar_per_ffe,
                      :bunker_cost => :dollar_per_ton
                    }

  Attribute_Units.each do |name, value|
    define_method(name) do
      read_attribute(name) / Units[Attribute_Units[name]][:si_factor]
    end

    define_method("#{name}=) do |assigned_value|
      write_attribute(name, assigned_value * Units[Attribute_Units[name]][:si_factor])
    end
  end