A tachometer is an instrument that measures the rotation speed of a shaft or disk. They are commonly used to measure the revolutions per minute of motors or other rotating machines.
Handheld tachometers are generally classified as contact type meters, and can be held against a rotating shaft to determine speed. Other measurement methods available on handheld tachometers include laser and optical coupler.
Handheld tachometers are frequently chosen when testing needs to be performed rapidly and often. Modern devices are sophisticated enough to measure up to 100,000 RPM and accurate within 6 thousandths of a percent. Other options are less accurate but can measure from several feet away.