An odometer is a device that is used for measuring the distance traveled by a vehicle. The odometer is usually situated in the vehicle's dashboard. The word "odometer" is derived from two Greek words meaning path and measure. An odometer may be digital or mechanical. Mechanical odometers usually comprise several cogs. Each cog on the mechanical odometer represents a numerical digit. The cogs turn according to the rotation of the wheels via a drive mechanism and cable. A windowed casing shows only the current mileage of the vehicle and not the mechanical parts. Digital odometers differ from mechanical odometers in that a computer chip is used to track mileage. The current mileage will be digitally displayed.
A vehicle may also have a trip meter or trip odometer. Unlike the regular odometer, the trip odometer can be reset at any point. A vehicle may have several trip odometers. Trip meters can be highly beneficial for recording the distance traveled over a specific period of time, making it easy to determine how many miles per gallon your vehicle is getting for each tank of fuel.
Resale value of a vehicle is often significantly affected by mileage. The lower the mileage on a vehicle, the higher the resale value. When an odometer is manually set to display a falsely deflated mileage, this is known as odometer fraud or clocking. The idea behind clocking is to make it look as though the vehicle has done less mileage than it actually has. In vehicles with a digital odometer, the mileage is stored in the engine control module. This makes it more difficult to change the mileage manually. To help combat odometer fraud, mechanics are required to maintain records of the odometer reading each time they service a vehicle. There are now many car service companies that use this information to help buyers determine whether odometer fraud has potentially occurred.
It is believed that a Roman engineer and architect developed the first odometer around 15 BC. The inventor of the seismograph, Chang Heng, also invented a type of odometer that could be used for measuring distance. Blaise Pascal invented the first modern prototype of an odometer in the 17th century. This device, known as the pascaline, was made up of wheels and gears. Each of the device's gears contained 10 teeth that would advance another gear when moved through a complete revolution. This is the same guiding principle that was later used in the mechanical odometer. In 1847, a group of Mormon pioneers traveling from Missouri to Utah invented an odometer known as the roadometer. The device was attached to a wagon wheel and was capable of counting the revolutions made by the wheel. Samuel Keen, in 1854, was the first individual to design an odometer for measuring distance driven. The device was attached to a carriage and measured distance as the wheels of the carriage turned.