Just remove all of the spark plugs, prop the throttle plate open (brick on the pedal would work), screw the compression tester into one of the spark plug holes, and crank the engine over for 4 or 5 revolutions. Note the reading and write it down. Repeat on all of the other cylinders.
You should see readings of 180 or so on a good engine.
This should be followed up with a wet test. This means going back and performing the test again but a small squirt of oil should be added to each cylinder before it’s tested.
Write down each reading on the wet test next to the one from the dry test.
If you see a noticeable jump upwards in the readings during the wet test (say 20, 30 PSI etc) then this is a sign of a ring problem.
It’s also possible to have good compression and still have a ring problem. The upper 2 compression rings may be fine but the oil control, or wiper ring, may be frozen in place due to oil coking, any prior overheating episodes, etc and is not wiping the cylinder wall of engine oil on the piston downstrokes. Hope this helps and if you do the test you might post back with the numbers. Best of luck.
(The reason I’m so critical of manuals, both factory and others, is that a lot of non-real world specs are published in there and I can only theorize is that these numbers are something a slide rule guy came up with. Erroneous compression numbers, oil pressure specs, you name it; a lot of it is flawed. I’ve got some factory Subaru service manuals that state 130 PSI of compression is the norm and that’s not just wrong; it’s absolutely ludicrous and downright laughable.)