A device used to determine the speed of rotation, typically of a vehicle’s crankshaft and usually in revolutions per minute. Also known as a "speedometer".

An instrument for measuring rotational speed by measuring the output voltage of a generator driven by the rotating unit.

1. An instrument that uses electronic elements to count the number of pulses (short durations of electrical current flows) applied to it.
2. An electronic circuit using electron tubes or equivalent devices for counting electric pulses or transient sharp changes in voltage, currents, or some other normally constant quantities in an electronic system.
3. An instrument capable of counting up to several million electrical pulses per second.