For your pointer to have moved that far from zero, it has either a loose or loosened friction fit to the shaft, or the gear train on the Bourdon tube (the oval copper flex tube) has jumped a few teeth due to accidental shock. I used to calibrate vacuum gauges at work. Some of the better ones have just a single screw to work with, which most people use to set the zero. There is typically no adjustment for 'span', which is how accurately the pointer travels along the scale with the pressure.
So, you can either adjust the screw or bend the flex link shown in the video posted above. It's probably only going to be accurate at one part in the range. You can set it to be accurate at zero psi, or adjust it to agree with another accurate gauge while it's reading a pressure in a range that's important to your process. You probably want it to be more accurate up around 2500 to 3000 psi.
If you adjust the gage to be accurate up in the middle or high end of it's range, the needle may not return exactly to zero at atmospheric pressure. This is the trade-off of a single point (zero only) calibration device.
On more sophisticated electronic sensors, for comparison, you have both a 'zero' and a 'span' adjustment that, after a few iterations of adjusting both, allows you to get perfect zero and accurate readings.
The 'C' shaped Bourdon tubes in these gages flex and try to straighten out slightly as the pressure goes up and down, and over time, they can fatigue and crack, or the solder joints in the tube start to leak. It's the same phenomenon that makes an air or water hose try to straighten out when it's pressurized.
Good luck with your repairs.
Feinwerk
