The dashboard instrument cluster in your car organizes a variety of sensors and gauges, including the oil pressure gauge, coolant temperature gauge, fuel level gauge, tachometer and more. But the most prominent gauge -- and perhaps the most important, at least in terms of how many times you look at it while you're driving -- is the speedometer. The job of the speedometer is to indicate the speed of your car in miles per hour, kilometers per hour or both. Even in late-model cars, it's an analog device that uses a needle to point to a specific speed, which the driver reads as a number printed on a dial.

Photo courtesy of Dreamstime A modern speedometer

As with any emerging technology, the first speedometers were expensive and available only as options. It wasn't until 1910 that automobile manufacturers began to include the speedometer as standard equipment. One of the first speedometer suppliers was Otto Schulze Autometer (OSA), a legacy company of Siemens VDO Automotive AG, one of the leading developers of modern instrument clusters. The first OSA speedometer was built in 1923 and its basic design didn't change significantly for 60 years. In this article, we're going to look at the history of speedometers, how they work and what the future may hold for speedometer design.

Types of Speedometers

Photo courtesy of Siemens VDO Automotive The speedometer has gone through many changes in the last century.

There are two types of speedometers: electronic and mechanical. Because the electronic speedometer is actually a relatively new invention -- the first all-electronic speedometer didn't appear until 1993 -- this article will focus primarily on the mechanical speedometer, or the eddy-current speedometer.

Otto Schulze, an inventor from Strasbourg, filed the first patent for the eddy-current speedometer in 1902. Schulze conceived of the revolutionary device as a solution to a growing problem. Cars weren't only becoming more popular, they were also traveling faster. The average automobile's top speed just after the turn of the 20th century was 30 miles per hour, slow by today's standards but sizzling fast at a time when much of the world still moved at the leisurely pace of a horse-drawn carriage. As a result, serious accidents began to increase dramatically.

Schulze's invention allowed drivers to see exactly how fast they were traveling and to make adjustments accordingly. At the same time, many countries established speed limits and used police officers to enforce them. Early solutions required automobiles to have speedometers with two dials -- a small dial for the driver and a much larger dial mounted so police could read it from a distance.

Video Gallery: Speedometers  Automakers often claim that their vehicles can do more than just get you from point A to point B, and drivers often wish they can push the speedometer on that shiny new sports car over a hundred, but few of them ever get the opportunity -- until now. See how automakers are offering exotic perks in this video from MediaLink. You can also learn more about cars and their parts in our original videos on how engines, turbochargers and clutches work.

In the next section, we'll look at this design to understand the parts of an eddy-current speedometer.