The Hangar 9® Micro Digital Tachometer is engineered using the latest technology. This handy tuning tool can measure the rpm of any engine equipped with a 2-, 3-, or 4-bladed propeller. RPM is displayed in up to four digits, with a range of up to 32,000 rpm. A long lasting 3V 220mAh lithium battery is included. The Micro Digital Tachometer’s auto shut-off feature prolongs battery life, and a low-battery icon indicates when the battery needs to be changed. It's also small enough to easily fit into your pocket.