calibrate your compression guage.

do a simple and easy check of your tool before testing your engine. crank it up to about 80 [ left guage] with nothing connected up to it. then check the right guage. mine shows it is off by 2 lbs. nice to know.

Gauge check...

Wendell and I noticed the same thing with his set of gauges.

You can bend the output gage towards/away from the face with your thumb. It will make the reading go up & down a few pounds. Now, which one do you believe, and does it matter? Not really.