No engine will have perfect sealing with 0 percent loss.
Air psi 15-20 to read loss 2nd gauge at 0psi, turn up air to hear leakage.
The percent of leakage should also be consistent across the cylinders.
The cylinder being tested must be placed at Top Dead Center (TDC).
5 - 10 percent loss indicates an engine in great to good running order.
10 - 20 percent loss can still run OK, but it’ll be time to keep an eye (or ear) on things.
20 + percent loss and it may be time for a teardown and rebuild.
30 + percent loss Major problems.
Any great differences indicate a problem in that cylinder.