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.