esto pocket pro compact optical tachometer. Testo 460 optically measures rpm with LED sighting and displays readings on a large backlit display. It features a convenient max/min function and is ideal for use with ventilators and shafts. The testo 460 is very handy, and easy to operate compact meter. Including calibration certificate. Protective cap for safe storage. Including wrist strap and belt clip. Display light. Reflective markers. 32 to 122 degree F operating temperature. 2 AAA batteries. 20 hours of battery life. Measures 4.5" length by 1.7" width by 1" height. Probe type RPM. Accuracy: +/- (0.02 percent of reading). Resolution: 0.1 rpm (100 to 999.9 rpm), 1 rpm (1000 to 29.999 rpm).