def convert_compound_unit_to_non_equivalent_unit!(new_unit)
      @unit.base_units.select do |base|
        base.unit.is_alternative_for? new_unit
      end.inject(self) do |quantity,base|
        factor = Unit.ratio(new_unit**base.index, base.unit**base.index)
        quantity.multiply!(factor).cancel_base_units!(base.unit)
      end
    end
def convert_compound_unit_to_non_equivalent_unit!(new_unit)
      @unit.base_units.select do |base|
        base.unit.is_alternative_for? new_unit
      end.inject(self) do |quantity,base|
        factor = Unit.ratio(new_unit**base.index, base.unit**base.index)
        quantity.multiply!(factor).cancel_base_units!(base.unit)
      end
    end
Conversion where self is a compound unit, and new unit is not an alternative
 to the whole compound but IS an alternative to one or more of the base units,
 e.g.,

   Unit.kilowatt_hour.to :second           #=> 'kilowatt second'