An odometer is an instrument that records the distance that a vehicle travels. It is different from a speedometer that measures the vehicle's speed or the tachometer that indicates the speed of rotation of the engine, although you may see all three on the dashboard of an automobile.

Timeline

Encyclopedia Britannia credits Roman architect and engineer Vitruvius with inventing the odometer in 15 BCE. It used a chariot wheel, which is of standard size, turned 400 times in a Roman mile and was mounted in a frame with a 400-tooth cogwheel. For each mile, the cogwheel engaged a gear that dropped a pebble into the box. You knew how many miles you went by counting the pebbles. It was pushed by hand, though it may never have been actually built and used.

Blaise Pascal (1623 - 1662) invented a prototype of an odometer, the calculating machine called a "Pascaline." The Pasacaline was constructed of gears and wheels. Each gear contained 10 teeth that when moved one complete revolution, advanced a second gear one place. This is the same principle employed in the mechanical odometer.

Thomas Savery (1650 - 1715) was an English military engineer and inventor who patented the first crude steam engine in 1698. Among Savery's other inventions was an odometer for ships, a device that measured distance traveled.

Ben Franklin (1706 - 1790) is best known as a statesman and writer. However, he was also an inventor who invented swim fins, bifocals, a glass harmonica, watertight bulkheads for ships, the lightning rod, a wood stove, and an odometer. While serving as Postmaster General in 1775, Franklin decided to analyze the best routes for delivering the mail. He created a simple odometer to help measure the mileage of the routes that he attached to his carriage.

An odometer called the roadometer was invented in 1847 by the Morman pioneers crossing the plains from Missouri to Utah. The roadometer attached to a wagon wheel and counted the revolutions of the wheel as the wagon traveled. It was designed by William Clayton and Orson Pratt and built by carpenter Appleton Milo Harmon. Clayton was inspired to invent the roadometer after developing his first method of recording the distance the pioneers traveled each day. Clayton had determined that 360 revolutions of a wagon wheel made a mile, he then tied a red rag to the wheel and counted the revolutions to keep an accurate record of the mileage traveled. After seven days, this method became tiresome, and Clayton went on to invent the roadometer that was first used on the morning of May 12, 1847. William Clayton is also known for his writing of the pioneer hymn "Come, Come, Ye Saints."

In 1854, Samuel McKeen of Nova Scotia designed another early version of the odometer, a device that measures mileage driven. His version was attached to the side of a carriage and measured the miles with the turning of the wheels.