No wires, cables, or fragile antennas . Data hold and low battery indications. Measures up to 12,000 RPM on conventional ignitions and up to 6,000 RPM on DIS ignition system . Just clamp over any spark plug wire. This tachometer gives accurate RPM readings quick and easy. This tachometer makes RPM measurements quick and easy. This is a very useful tool for tune-up and other diagnostic work where accurate RPM readings are required. Just clamp over any spark plug wire and get accurate RPM on conventional or DIS ignition systems. The unit also features a data hold function. The large 2000 count LCD display shows; RPM, function, data hold indication and low battery indication. Powered by one 9 volt battery.