Originally Posted by Bicyclops
The incorrect reading would only be during the calibrated orifice test conducted before the actual differential pressure tests on the cylinders. This test is to determine the lowest acceptable reading for today's compression test and won't affect the cylinder test. You might be surprised how low a compression reading this test will show as being acceptable.
Comparison with the "calibrated" leakage orifice is a Continental standard, not Lycoming. And no, I am not surprised.
Perhaps it would be best to read the appropriate manufacturer's guidance?
Let's make this easy. Per the OP's question, choose either below, the difference being the T-handle extension, which offers hand tightening. Both are 0.040" testers for flat Lycoming and Continental. Compare the cylinder reading with the test orifice reading for Continental. Ignore the test orifice for Lycoming. In either case, interpret results per Continental SB 03-3 or Lycoming SI 1191A.
These are ATS brand tools. Precise accord with Continental SB 03-3 would require purchasing the equivalent tool made by Eastern