Manifold Vacuum Advance what am I not getting?

Regarding compression test. I don’t know what to believe. I double checked my compression gauge to that of my pressure gauge on my spray gun set up on my compressor, which I think is pretty decent. They were identical. my guess is the gauges OK but I did only compared to at 80 psi 200 psi could be off.
Also, I did this with the engine cold. It’s just too ******* hot working in the garage over a hot engine. I also did not add any oil or anything to the cylinder. And in some instances, some of the plugs in and some of the plugs were out I don’t know if that makes a difference for this type of test.