Oil Pressure Gauge calibration?

[The Red Baron]

Hi.

I've noticed my oil pressure reading is a bit low:30psi cold/<20psi hot.

I've tested using a mechanical gauge instead of the electric sender and the difference is huge: 55psi cold, which is what I'd expect.

So its either the sender or the gauge itself. The gauge reads below zero with ignition on and if it read zero the oil pressure reading would be higher and closer to the truth.

Is there any way to adjust the needle to read zero with power on? I've got the gauge out but it looks to be a sealed unit.

Thanks for any advice.