Relative compression test using an oscilloscope
This is a screenshot of a relative compression test using the Autel Maxiscope. From this, we can see that one cylinder has slightly lower compression. Because I have synced cylinder 1 on a car with a 1-3-4-2 firing order, I can see that cylinder 2 is lower than the others in this capture.
While this test provides good direction, further tests would be required for a definitive diagnosis.
The capture came from a VW Golf that had an intake valve seating issue in cylinder 2. I also performed a leak-down test to confirm, but this initial test took less than 10 minutes from setup to conclusion and provided great information.
A relative compression test carried out on a less expensive Snap-On Vantage Pro. But gives the same results.
Some links with more information
https://www.youtube.com/watch?v=0P0CPRFLmww
https://autoditex.com/page/relative-compression-test-67-1.html