Log in

An odometer (often known colloquially as a mileometer or milometer) is a device used for indicating distance traveled by an automobile or other vehicle. It may be electronic or mechanical. The word derives from the Greek words hodós, meaning 'path' or 'way', and métron, 'measure' (an older name for this device is hodometer).


Mechanical odometers usually appear as a row of wheels with an edge of each wheel exposed to the driver. There are digits written on the edges of these wheels. A mask obscures these wheels from view, except for one row of digits which can be seen through a window in the mask.
On older cars, odometers could only indicate up to a value of 99,999; in the early days of the automotive industry this was adequate. With continuous improvements, modern vehicles now survive to travel several hundred thousands of miles/kilometers. At 100,000, the odometer would restart from zero. This is known as odometer rollover. Newer cars have odometers that can indicate up to a value of 999,999.

Possibly the first evidence for the use of an odometer can be found in the works of Pliny (NH 6. 61-62) and Strabo (11.8.9). Both authors list the distances of routes traveled by Alexander the Great (r. 336-323 BC) as measured by his bematists Diognetus and Baeton. However, the high precision of the bematists's measurements rather indicates the use of a mechanical device. For example, the section between the cities Hecatompylos and Alexandria Areion, which later became a part of the silk road, was given by Alexander's bematists as 529 English miles long, that is with a deviation of 0.4% from the actual distance (531 English miles). From the nine surviving bematists' measurements in Pliny's Naturalis Historia eight show a deviation of less than 5% from the actual distance. Three of them even less than 1%. Since these minor discrepancies can be adequately explained by slight changes in the tracks of roads during the last 2300 years, the overall accuracy of the measurements implies that the bematists already must have used a sophisticated device for measuring distances, although there is no direct mentioning of such a device.

An odometer for measuring distance was first described by Vitruvius around 27 and 23 BC. The actual invention may have been by Archimedes of Syracuse during the First Punic War. Hero of Alexandria describes a similar device in chapter 34 of his Dioptra. The machine was also used in the time of Roman Emperor Commodus (c. 192 AD), although after this point in time there seems to be a gap between its use in Roman times and that of the 15th century in Western Europe.

The odometer of Vitruvius was based on chariot wheels of 4 feet (1.2 m) diameter turning 400 times in one Roman mile (about 1400 m). For each revolution a pin on the axle engaged a 400 tooth cogwheel thus turning it one complete revolution per mile. This engaged another gear with holes along the circumference, where pebbles (calculus) were located, that were to drop one by one into a box. The distance travelled would thus be given simply by counting the number of pebbles. Whether this instrument was ever built at the time is disputed. Leonardo da Vinci tried to build it according to the description but failed. Later, Ben Franklin invented his own version. Benjamin Franklin invented a simple odometer when he was going on trips in carriages. He wanted to know how far he was going, and the speed he was travelling.

The odometer as used in modern systems, where a separate gear controls each digit, was invented in 1847 by William Clayton with help from Orson Pratt. Clayton, a Mormon Pioneer, developed the odometer (dubbed the "roadometer") to keep track of wheel revolutions on the pioneer wagons. The odometer had at least two gears, including one which turned every quarter-mile and one which turned every ten miles.