mileometer n : a meter that shows mileage traversed [syn: odometer, hodometer, milometer]

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).

Recently, exercise enthusiasts have observed that an advanced Global Positioning Satellite (GPS) receiver (GPSr) with an odometer mode serves as a very accurate pedometer for outdoor activities. While not truly counting steps (no pendulum is involved) an advanced GPSr odometer can reveal the accurate distance traveled to within 1/100th of a mile (depending on the model, perhaps 1/1000th of a mile). 1/1000th of a mile is approximately the distance of a single pace or 2 steps.

The modern definition of the international mile traces back to the Roman military method of keeping track of how far a soldier had traveled on foot. The Latin "mille passus" is literally "a thousand paces" where 1 pace = 2 steps. The international mile (5,280 feet) is somewhat longer than the original Roman mile (4,854 feet). As with the mile, the definition of "foot" has changed many times.

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

Synopsis

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. New cars since 1980 have odometers that can indicate up to a value of 999,999.

A common form of fraud is to tamper with the reading on an odometer; this is often referred to as clocking. This is done to make a car appear to have been driven less than it really has been, and thus increase its apparent market value. Many new cars sold today use digital odometers that store the mileage in the vehicle's engine control module making it difficult (but not impossible) to manipulate the mileage electronically. With mechanical odometers, the speedometer can be removed from the car dash board and the digits wound back, or the drive cable can be disconnected and connected to another odometer/speedometer pair while on the road. Modern odometers now add mileage driven in reverse to the total as if driven forward, to accurately reflect the true total wear and tear on the vehicle.

Most modern cars also include a trip meter, also referred to as a trip odometer. Unlike the odometer, a trip meter is designed to be reset at any desired point in a journey, making it possible to record the distance travelled in any particular journey or part of a journey. It was traditionally a purely mechanical device but, in most modern vehicles, it is now electronic. Luxury vehicles often have multiple trip meters. Most trip meters will show a maximum value of 999.9. There are practical uses for this:

Record the distance traveled on each tank of fuel, making it very easy to accurately track the energy efficiency of the vehicle.

When following driving directions, one can reset it to zero at each instruction to be sure when one has arrived at the next turn.

History

The odometer was also later invented in ancient China, possibly by the profuse inventor and early scientist Zhang Heng (78–139 AD) of the Han Dynasty (202 BC–220 AD). Zhang Heng is often accredited with the invention of the first odometer device in China, an achievement alongside earlier contemporaries Archimedes and Heron of Alexandria from the Hellenized West. By the 3rd century (during the Three Kingdoms Period), the Chinese had termed the device as the 'jì lĭ gŭ chē' (記里鼓車) , or 'li-recording drum carriage' (Note: the modern measurement of li = 500 m/1640 ft). Chinese texts of the 3rd century tell of the mechanical carriage's functions, and as one li is traversed, a mechanical-driven wooden figure strikes a drum, and when ten li is traversed, another wooden figure would strike a gong or a bell with its mechanical-operated arm. The historian Joseph Needham asserts that it is no surprise this social group would have been responsible for such a device, since there is already other evidence of their craftsmenship with mechanical toys to delight the emperor and the court. There is speculation that some time in the 1st century BC (during the Western Han Dynasty), the beating of drums and gongs were mechanically-driven by working automatically off the rotation of the road-wheels. The passage in the Jin Shu expanded upon this, explaining that it took a similar form to the mechanical device of the South Pointing Chariot invented by Ma Jun (200–265, see also differential gear). As recorded in the Song Shi of the Song Dynasty (960-1279 AD), the odometer and South Pointing Chariot were combined into one wheeled device by engineers of the 9th century, 11th century, and 12th century (refer to South Pointing Chariot). The Sun Tzu Suan Ching (Master Sun's Mathematical Manual), dated from the 3rd century to 5th century, presented a mathematical problem for students involving the odometer. It involved a given distance between two cities, the small distance needed for one rotation of the carriage's wheel, and the posed question of how many rotations the wheels would have in all if the carriage was to travel between point A and B.

Next, there is fixed (on the same shaft) a small horizontal wheel (hsiao phing lun) 3.3 inches in diameter and 1 ft in circumference, having 10 cogs 1.5 inches apart. (Engaging with this) there is an upper horizontal wheel (shang phing lun) having a diameter of 3.3 ft and a circumference of 10 ft, with 100 cogs, the same distance apart as those of the small horizontal wheel (1.5 inches).

When the middle horizontal wheel has made 1 revolution, the carriage will have gone 1 li and the wooden figure in the lower story will strike the drum. When the upper horizontal wheel has made 1 revolution, the carriage will have gone 10 li and the figure in the upper storey will strike the bell. The number of wheels used, great and small, is 8 inches in all, with a total of 285 teeth. Thus the motion is transmitted as if by the links of a chain, the "dog-teeth" mutually engaging with each other, so that by due revolution everything comes back to its original starting point (ti hsiang kou so, chhuan ya hsiang chih, chou erh fu shih).

Modern History

In modern times, Andre Sleeswyk was able to make a working model of an odometer using gears similar to the Antikythera mechanism as opposed to the traditional cogwheel.

The odometer as used in modern systems, where a separate gear controls each digit, was invented 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.

Law

The resale value of a vehicle is often strongly influenced by the number of miles or kilometres a passenger vehicle has on the odometer, yet odometers are inherently insecure because they are under the control of their owners. Many jurisdictions have chosen to enact laws which penalize people who are found to commit odometer fraud. In the US (and many other countries), vehicle maintenance workers are also required to keep records of the odometer any time a vehicle is serviced. Companies such as Carfax then use this data to help potential car buyers detect whether odometer rollback has occurred.

Sport

Odometers feature in some sports, both amateur and professional. Odometers designed for cycling help cyclists to determine distance cycled and often other information. (See cyclocomputer) Professional rally cars are usually equipped with a purpose-built odometer with an adjustable factor. This factor determines the number of wheel rotations in, say, one kilometre or one mile. Amateur rally cars are often also equipped with purpose-built adjustable odometers for regularity rallying.

See also

• Hubometer
• Speedometer
• Surveyor's wheel
• Tachograph
• Tachometer
• Taximeter
• Pedometer
• Counter

References

• Sleeswyk, André Wegener "Vitruvius' Odometer", Scientific American 245.4 (October, 1981), pp. 188-200
• Sleeswyk, Andre W. "Vitruvius' Waywiser", Archives internationales d'histoire des sciences Vol. 29 (1979), pp. 11-22.
• Donald W. Engels: Alexander the Great and the Logistics of the Macedonian Army, Los Angeles 1978, p.157f.
• Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books, Ltd.

Notes

External links

• Vitruvius' description
• Vitruvius' description - Project Gutenberg
• Shockwave-Animation: The Odometer of Vitruv
• History of the Odometer
• Odometry in Determination of the Position of an Autonomous Mobile Vehicle
• Odometre.com
• DLand Pro A digital odometer's manufacturer
• Relojería LEO A digital odometer's manufacturer
• "How Odometers Work" by Karim Nice