Measurement.define(:µg) do |unit|
  unit.alias :microgram, :micrograms
  unit.convert_to(:t) { |value| value / 10_000_000_000.0 }
  unit.convert_to(:kg) { |value| value / 10_000_000.0 }
  unit.convert_to(:hg) { |value| value / 1_000_000.0 }