How Speedometers Work

The Future of Speedometer Design

A head-up speedometer display
A head-up speedometer display
Photo courtesy of Siemens VDO Automotive

­­One of the big disadvantages of an instrument cluster is its location. A driver must look down to see the dials, which means his eyes are off the road for at least one second. In that one second, the car travels about 46 feet if it's moving at 30 miles per hour.

Siemens VDO is addressing this issue with a head-up display that is projected onto the windshield by mirrors. To the driver, the display appears to float above the engine hood, about six feet away. Vehicle speed will be one of the key elements of the display, but it can contain any element found in a normal instrument cluster. It can also integrate orientation aids that use images from infrared cameras to detect and display an outline of the road ahead. For a technology that dates back almost 100 years, that's a significant change for the better.


For more information on speedometers, cars and related topics, check out the links below.


­Related HowStuffWorks Articles

More Great Links


  • “100 Years of Speedometers — The History of Driver Information,” November 7, 2002. Found online at:
  • “Automating Speedometer Calibration,” by Ganesh Devaraj, S.B. Rajnarayanan, A. Senthilnathan and S.R. Anand. Evaluation Engineering. Found online at
  • Encyclopedia Britannica 2005, s.v. “eddy current.” CD-ROM, 2005.
  • Encyclopedia Britannica 2005, s.v. “flexible shaft.” CD-ROM, 2005.
  • Encyclopedia Britannica 2005, s.v. “tachometer.” CD-ROM, 2005.
  • Erjavec, Jack. "Automotive Technology: A Systems Approach." New York: Thomson Delmar Learning. 2005.
  • “From speedometers to modern instrument clusters,” by Gerhard Wesner. Automotive Engineering International, January 2005. PDF download at
  • Inner Auto Parts Web Site:
  • Tire Size Calculator
  • The National Watch and Clock Museum
  • Siemens VDO Automotive Web Site