Tachometer and Tach Block

A tachometer is designed to give the speed of a rotating part in revolutions per minute (rpm). For automotive use, the tachometer is made for measuring the speed of the engine. One lead of the tachometer is connected to the primary terminal of the distributor. The other lead is connected to ground. The control is set for low range to test curb idle and fast idle. The control is set for high range to make tests at speeds above 1200 rpms. A "tach block" is a block with exposed terminals to hook up test equipment or to connect to an electrical circuit.