No compression-next move?

try another gauge?
If the valves are moving, and split overlap is close, I have never seen zero psi

If you stick anything in the hole, be aware what can happen if the valves begin to open.
I use a different method. I take the gauge off the compression tester (Quick disconnect),and screw the hose back into the plughole. Then I stick the other end in my mouth, but do not make the mistake of sealing it hard and cranking it with the starter; you could blow your eardrums out!!.No, instead, gently motor the engine by hand. You will be able to find TDC compression pretty close........ if everything is as it should be; certainly close enough if the damper is marked.