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, or, colloquially,

 

GPS used as odometer:

A  GPS with odometer mode is also an excellent and inexpensive means to verify proper operation of both the speedometer and odometer mounted in a vehicle.