ATD Tools Pro Laser Tachometer is an ideal tool for easy and accurate measurement of RPM in almost any environment. High intensity laser beam not affected by shop light, detects RPM from up to 6 feet away and measures up to 99,999 RPM in 1 RPM increments and can be used to measure RPM on coil-on-plug as well as diesel engines. Simple operation, just aim at reflective mark to get RPM memory function that saves maximum and minimum RPM readings.