High end measuring instrument for your engine.
As in a motor or other machine, a Tachometer is an instrument that measures the rotation speed of a shaft or disk. Revolutions per minute (RPM) are typically displayed on a calibrated analogue dial, but digital displays are becoming more common. The name derives from two Greek words, τάχος or táchos referring to speed and μέτρον or métron meaning measure. These devices are generally used for measuring engine and vehicle performance.