Measurement.define(:'mi²') do |unit|
  unit.alias :mi2, :'mi*mi', :'sq mi', :'square mile', :'square miles'
  unit.convert_to(:fur2) { |value| value * 64.0 }
  unit.convert_to(:ch2) { |value| value * 6_400.0 }
  unit.convert_to(:yd2) { |value| value * 3_097_600.0 }