Odometer • How Odometers Work

Related Innovations • Automobile

An an odometer records the distance that a vehicle travels. A speedometer measures the speed of a moving vehicle. A tachometer indicates the speed of rotation of the engine. 

Vitruvius
According to Encyclopedia Britannia, "About 15 BC, the Roman architect and engineer Vitruvius mounted a large wheel of known circumference in a small frame, in much the same fashion as the wheel is mounted on a wheelbarrow; when it was pushed along the ground by hand it automatically dropped a pebble into a container at each revolution, giving a measure of the distance traveled. It was, in effect, the first odometer."

Chang Heng
Chang Heng the inventor of the known seismograph, also invented an odometer that had a figure that struck a drum as each li or 0.5 km went by to measure distance.

Blaise Pascal
Blaise Pascal (1623 - 1662) invented a prototype of an odometer, a 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 principal employed in the mechanical odometer.

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

Ben Franklin - Odometer used to Measure Postal Routes
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 armonica, 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 invented a simple odometer to help measure the mileage of the routes that he attached to his carriage. 

William Clayton, Orson Pratt, Appleton Milo Harmon - Odometer called the Roadometer
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. 

William Clayton was inspired to invent the roadometer by his first method of recording the distance the pioneers travelled 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 travelled. After seven days, this method became tiresome and Clayton went on to invent the roadometer, 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." 

"I walked some this afternoon in company with Orson Pratt and suggested to him the idea of fixing a set of wooden cog wheels to the hub of a wagon wheel, in such order as to tell the exact number of miles we travel each day. He seemed to agree with me that it could be easily done at a trifling expense." 

"Brother Appleton Harmon is working at the machinery for the wagon to tell the distance we travel and expects to have it in operation tomorrow, which will save me the trouble of counting, as I have done, during the last four days."

"About noon today Brother Appleton Harmon completed the machinery on the wagon called a 'roadometer' by adding a wheel to revolve once in ten miles, showing each mile and also each quarter mile we travel, and then casing the whole over so as to secure it from the weather." ~ From William Clayton's Journal 

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