compression check ?

Depending on the quality of the gauge, the numbers are really only representing relative pressures, which shouldn't vary more than 10% on an engine with miles..

In my shop, we have 3 compression guages, a Mac, a Snap-on, and a $39 budget guage,, they are all different, on the same engine/cyl, - by up to 18 lbs. but they all will show a cylinder imbalance..

but try to figure compression ratio,,.. anyone's guess is good.. my .02