Measurement: Photo Tach ( 2.5 ~ 99, 999 RPM), Contact Tach ( 0.5 ~ 19, 999 RPM), Surface Speed ( 0.05 ~ 1, 999.9 m/min); Dual Function unit with both Contact and Non-contact capabilities; Provides fast and accurate RPM (revolutions per min) measurements of rotating objects; Internal memory recalls maximum, minimum values as well as last value stored; It has Auto Ranging, detecting distance of up to 500mm or 20inch and accuracy of ±( 0.05 % +1digit).