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Speedometers display the speed at which a vehicle is traveling. 

  • speedometer in the instrument cluster shows the driver how fast the vehicle is moving commonly displaying speed measurement in mph. Many speedometers are driven from the transmission output shaft by a set of gears. The driven gear fastens to a flexible shaft or speedometer cable. It runs from the transmission putout shaft to the back of the speedometer head.
  • Inside the speedometer, the cable turns a shaft with a small magnet on it. The rotating magnetic field produces a varying pull on the metal ring surrounding the magnet. 
  • A pointer is attached to the metal ring. As the magnetic field spins, it causes the ring to overcome a light spring and swing the magnetic field. This moves the pointer which then indicates the car speed. The faster the car speed, the faster the magnet spins, and the farther the pointer moves