A tachometer is used to calculate the angular speed of a rotating shaft in revolutions per minute. Tachometer gauges are used in factory and manufacturing operations where timing and precision are imperative to consistent and quality production. Conveyors and plastic injection molding machines heavily rely on tachometers to measure and control the speed of operation. Tachometers are also used in packaging operations where several different functions immediately follow each other and each requires a change in speed. Automobile tachometers measure the car engine’s rpm.