This sounds like a defective gauge. Check face plate behind pointer for damage. Take gauge apart (normally two screws on back plate) and straighten if necessary. The pointer can be calibrated by pulling it off the stem. Use two flat head screwdrivers and place the blades on either side of the pointer close to the stem (remove the cover from the gauge). Pry the pointer off being careful not to lose it. Reset the pointer back on the stem at zero and thump with finger or end of screwdriver. Hopefully it will stay. Turn on cylinder and at 70F, should read around 850 PSI.
Scott Zuhse, Instructor
Micro Matic Dispense Institute