Make sure you don't leave the comrpession tester pressurized for too long after taking the reading. I did a compression test today and left the tester in the head, still pressurized, for about 5 mins and while i was doing something else, I heard a loud POP and saw the tester go flying across the garage. The hose that went into the head came apart right at the fitting, leaving the fitting stuck in my head. Getting it out was, um, fun. Anyway, this was a $29 Actron tester that I got from Autozone. Maybe the more expensive ones work better:dunno: