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A speedometer is the device in a vehicle that measures and displays the speed, and is essential for safety purpose on roads and highways around the world. The speedometer on a car, truck or motorcycle tells the driver how fast the vehicle is moving at any given time by instantaneously measuring the speed on the ground. The device is now digital on many vehicles, and takes different incarnations as the motorcycle speedometer or bike speedometer.
Though the speedometer came to be seen as standard by the end of the 20th century, the device was not required on vehicles in the early 1900s. The car speedometer became standard in 1910, still in the infancy of the automobile, and has been a mainstay ever since. The regular speedometer and motorcycle speedometer have both maintained staying power on the dashboard of the vehicle and positioned within clear sight of the driver.
Many of these devices are situated right behind the steering wheel on your car, and can be read with a quick glance down from the road. Some are digital, and can be read with two or three numbers reflecting your speed; while others require a rotating arm like a clock. On most cars, the arm moves from the low speed on the left to the higher speeds on the right. Many of these speedometers reflect speeds from zero miles per hour to as high as 140 miles (225 km) per hour; while others stop around the safe limit of 90 miles (145 km) per hour.
Invented in 1888 by the Croatian scientist Josip Belusic and first called a velocimeter, the speedometer has been seen on various other forms of transportation as well. The digital speedometer on an airplane is called a airspeed indicator, while the one on a boat is referred to as the pit log.
Speedometers have an error tolerance of around 10% as the car and the device both age. The device is read by a flexible cable that is attached to the car’s transmission, which indicates how quickly the vehicle is moving. More recent electronic speedometers are fitted with magnets and field sensors to the drive shaft to deliver to the driver the speed of the vehicle. Even on bicycles, speedometers measure the time between the revolutions of the wheel to tell the rider how fast they are going.