Tachometer
Instrument measuring the rotation speed of a shaft or disk / From Wikipedia, the free encyclopedia
Not to be confused with Tachograph, used for recording vehicle data, Tacheometer, used for surveying, or Tachymeter (watch), used on watches.
"Revolution-counter" redirects here. For opposition to a fundamental change in power, see Counter-revolution.
"Tach" redirects here. For other uses, see Tach (disambiguation).
A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine.[1] The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common.
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The word comes from Greek τάχος (táchos "speed") and μέτρον (métron "measure"). Essentially the words tachometer and speedometer have identical meaning: a device that measures speed. It is by arbitrary convention that in the automotive world one is used for engine revolutions and the other for vehicle speed. In formal engineering nomenclature, more precise terms are used to distinguish the two.