Ideal tool for easy & accurate measurement of rpm in almost any environment High intensity laser beam not affected by shop light, detects rpm from up to 6 ft. away Measures up to 99,999 rpm in 1 rpm increments and can be used to measure rpm on coil-on-plug & diesel engines Simple operation, just aim at reflective mark to get rpm Memory function saves maximum and minimum rpm readings Zippered case, reflective tape, instructions and 9V battery included