TACHOMETER

(tach) A device used to indicate the speed of the engine in rpm. The tachometer is mounted on or near the dashboard (some even appear on the hood and others in a heads-up display on the windshield ). It helps the driver to know the optimum rpm for changing gears on manual transmissions . A tachometer is also a diagnostic device which a mechanic uses to determine idle speed and other carburetor and running settings.