It's possible to get widely different compression pressures just by switching gauges. The percentage difference between cylinders is the important thing to watch, with 10% being a maximum allowable difference in most cases.
Also, doing a "wet" compression check by squirting a little oil into the cylinder before cranking will often raise the pressures noticeably. If that's the case, leakage past the piston rings is probably the source of a low reading.
Use a well-charged battery, remove all the plugs, disable the ignition, and block the throttle open. Let each cylinder "hit" about four times, and record each reading, then compare the pressures.
Jerry
