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 noun 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.

Odometers were first developed in the 1600s for wagons and other horse-drawn vehicles in order to measure distances traveled.

In 1645, Blaise Pascal invented the pascaline. Though not an odometer, the pascaline utilized gears to compute measurements. Each gear contained 10 teeth. The first gear advanced the next gear one position when moved one complete revolution, the same principle employed on modern mechanical odometers.

Odometers were developed for ships in 1698 with the odometer invented by the Englishman Thomas Savery. Benjamin Franklin, U.S. statesman and the first Postmaster General, built a prototype odometer in 1775 that he attached to his carriage to help measure the mileage of postal routes. In 1847, William Clayton, a Mormon pioneer, invented the Roadometer, which he attached to a wagon used by American settlers heading west. The Roadometer recorded the distance traveled each day by the wagon trains. The Roadometer used two gears and was an early example of an odometer with pascaline-style gears in actual use.

In 1895, Curtis Hussey Veeder invented the Cyclometer. The Cyclometer was a mechanical device that counted the number of rotations of a bicycle wheel. A flexible cable transmitted the number of rotations of the wheel to an analog odometer visible to the rider, which converted the wheel rotations into the number of miles traveled according to a predetermined formula.

In 1903 Arthur P. and Charles H. Warner, two brothers from Beloit, Wisconsin, introduced their patented Auto-meter. The Auto-Meter used a magnet attached to a rotating shaft to induce a magnetic pull upon a thin metal disk. Measuring this pull provided accurate measurements of both distance and speed information to automobile drivers in a single instrument. The Warners sold their company in 1912 to the Stewart & Clark Company of Chicago. The new firm was renamed the Stewart-Warner Corporation. By 1925, Stewart-Warner odometers and trip meters were standard equipment on the vast majority of automobiles and motorcycles manufactured in the United States.

Source: Odometer from Wikipedia

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