You can also do a dry, then "wet" comp test as a way to evaluate rings.
Make one lap around the engine with the comp tester on dry cylinders. Write down your comp numbers for each cylinder. Then get a little bottle with a pointy cap, the type of cap that comes on 90wt gear oil bottles. Give each cylinder an ounce or 2 squirt of engine oil in through the spark plug hole before threading in the comp tester. Repeat the test for each cylinder and record the "wet" numbers.
If you see a big difference in pressure on a particular cylinder(s)between your dry and wet numbers, this would indicate a ring/cylinder problem. The oil will typically raise the number a bit, but if you have a low pressure cylinder and the oil trick doesn't bring it up into the range of the other cylinders, this points to valve issue.
