Extech 461895 Combination Photo/Contact Tachometer Unique display where characters reverse direction depending on measurement mode you are in Microprocessor based with quartz crystal oscillator to maintain high accuracy Tachometer memory stores last, max and min readings Provides wide RPM (photo and contact) and Linear Surface Speed (contact) measurements Accurate to 0.05 percent with max resolution of 0.1rpm in either photo or contact mode