An odometer or odograph is an instrument that indicates distance traveled by a vehicle, such as a bicycle or automobile. The device may be electronic, mechanical, or a combination of the two. The word derives from the Greek words hodós ("path" or "gateway") and métron ("measure"). In countries where Imperial units or US customary units are used, it is sometimes called a mileometer or milometer, the former name especially being prevalent in the United Kingdom and members of the Commonwealth.