Hello, well when I first took it out of the box the plastic screen cover had come un glued. I stuck it back on and it has stayed in place. The tach works perfectly. I checked the tach against my scan tool on my truck at idle. Both were basically indicating the same RPM. The trucks idle changes a few RPM. My lawn mower was 3541 RPM and rock solid. In my opinion this is a handy tool for the money. Knocked one star off for the weak screen glue.