TACHOMETER Features: Low cost contact and non-contact 2 in 1 combo tachometer in the market  Two ways to power on/off Safe and easy to get rotation speed! Non-contact measurement by red LED beam Contact rotating object via convex or concave contact tips Auto power off in 20 mins inactivity Hold function freezes current reading Four rotation speed units are selectable in contact mode:rpm, m/min, ft/min, yd/min. Sleep mode can be disabled(the meter turns off automatically after 20 mins inactivity.it can be disabled in follow the operation manual. ) low battery icon indicates weak power.