Compression pressures using a gauge are only a guide to follow any wear in a particular engine. Even this only applies if you use the same gauge all the time or if you want to compare figures with someone else then they have to be using the exact same gauge as well. All gauges have a dead volume inside them which includes whatever tubing leads from the engine to the part inside the gauge that takes the measurement. All of this dead volume of air has to be compressed which gives the affect of having a much larger combustion chamber volume. Basically this means that the smaller the engine you test the lower the pressure is going to read.

In theory, if the engine had 10:1 compression then the gauge should read about 150psi (disregarding any heating of the air caused by the compression). The dead volume reduces this figure considerably. The other thing is that compression only starts when the exhaust port closes so instead of compressing the full swept volume of the engine you're only compressing maybe 3/4 of the swept volume. Combine the dead volume loss with the swept volume loss and instead of reading 150psi you read about 60psi, in other words it's just a guide.

The best compression tester is your fingers. Turn the engine up against compression until it just starts to get into the pinch area and hold it there. If the engine is in good condition you should feel the compression trying to push the piston back down for several seconds. Basically that's a leak down test. The rule of thumb for old iron piston engines was that if you could still feel at least some compression after 5 seconds then it was fine. An ABC should hold for longer than you have patience if you put the piston up into the pinch. I did this with a Rossi and after 45 minutes I figured that was long enough . Putting the piston into the pinch isn't a fair test though because there's no pinch once warm.