A car speedometer measures speed: how fast the car is moving. Speedometers measure speed in miles per hour or kilometers per hour. Some gauges display both readings.
Speedometers have been standard equipment in automobiles since 1910. For most cars, a pointer indicates the speed on a dial.
Speedometers do not measure velocity. Velocity indicates how fast something is changing position. It is a "vector quantity," which means it involves two measurements. Both an object's speed and its direction are included in velocity. For instance, a car traveling from New York to California might have a speed of 55 mph. However, its velocity is 55 mph, west.