The air in the cylinders heats up as a result of being compressed. If you could compress it and then hold it there and wait for it to cool back off to ambient, then the gauge would tell you the static CR. Obviously this is not practical. If the engine is even a little bit warm, the gauge reading can go even higher. An engine with a small cam will give higher readings than an otherwise identical one with a large cam, because the extra duration will bleed off pressure at the beginning of the intake stroke.
All you can do with a compression test os check for consistency. It's highly unlikely that all cylinders would be worn exactly the same amount; so as long as they're all pretty close, odds are the engine is in good shape or at least not grossly defective.
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