Rotax 912 Compression Test
I used a differential compression tester; the same as used on the Lycoming/Continental Engines.
Just be darn careful that you have the piston on top dead center of the compression stroke and a qualified/experienced person holding the prop; before applying air pressure to the cylinder being tested.
I also highly recommend balancing the carburetors with a manometer; you won't believe the difference in how well that engine can run with balanced carb's. As far as i am concerned--the Rotax engine is a well proven and excellent engine.