Checking compression

It should reach max pressure in ~4 compressions, but I would just keep cranking until the needle stops going up regardless. I go ~10 times in my M-B diesels. Some say a good engine will reach the final pressure in less cranks, but I don't see a reason. It is probably more dependent upon your compression gage. Also, crank w/ the throttle and choke held open.

The manual specs a variation between cylinders. Something like 10 psi. I would be more concerned that all cylinders measure good, which is probably >115 psig for a typical slant. 145 psig would be like new. The values depend a lot on the camshaft installed.

I think the spec is for a warm engine. Even more important is that it has run in the last week so that oil is everywhere. If the engine has sat for years, there may be no oil to seal the rings. If it won't start, you can pour a tablespoon of oil thru each spark plug hole. That is also one way to infer "bad rings", but a bit tricky to call.