Measurement.define(:ml) do |unit|
  unit.alias :milliliter, :milliliters
  unit.convert_to(:kl) { |value| value / 1_000_000.0 }
  unit.convert_to(:hl) { |value| value / 100_000.0 }
  unit.convert_to(:dal) { |value| value / 10_000.0 }