The automotive type compression tester has a Schrader type valve that accumulates the highest pressure. When done, you press the button and it releases the pressure.

As said earlier, To take a chainsaw and pull it through with the cord five or six times or until the pressure doesn't rise any more generally gets up to around 150 lbs.

A chainsaw with close to 100 lbs will be harder to start and be weak in the power department.