Hobbico markets two compression gauges. HCAP2600 is for .10 to .60 engines. HCAP2601 is for .60 on up. I bought one when I was just starting out, and never used it much. Flipping the prop through will tell you the same thing. It was suggested here at RCU, that a good way to use them is to check the reading on a new engine, keep this on file, then use it as a benchmark to document wear.