For what we do, ie uncertified work, and aircraft tester is fine. Set it at 80 lbs and do the math to reach the number based on 100. Or, take it up to 100 lbs and read accordingly. It is leak down you are after. This is the amount of air escaping from the cylinder. Tune your ear to know what you are hearing. Air through the exhaust is an exhaust valve leaking. Air in the intake is a intake valve leaking. Air from the oil tank is rings. Some air and high compression number are OK, lots of leaking air and low leak down numbers make your mechanic happy. Number way off on that cylinder is cause for further looking. 80/80 is the highest. 80/60 is a cylinder at 75% 80/78 is 97.5% efficiency. Prices on these testers from Aircraft Too Supply (
www.aircraft-tool.com) run from $60 to 110.