Here is the link for a user manual for a typical compression tester.
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http://www.iequus.com/Content/Support/Manual/compress.pdf
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As far as the numbers, the actual values of the readings is not as important as the spread between the high and low numbers for each cylinder and the percentage difference.� What you are looking for is the cylinder with poor compression, which may be due to various reasons such as piston rings or valves.� 
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Note the warning�"For electronic or conventional breaker point ignition systems: Remove the high tension (coil) wire from the distributor cap and connect to a known good ground to avoid spark discharge, or disconnect coil primary connector."

Cheers!
Stuart