Please pardon my 82 year old foggy brain.
I sat this morning at KNPA (field elevation 15 feet or so) in the PA34.
Had checked the local atmospheric pressure for Pensacola, and it was 29.85 HG
Checked the pressure on the altimeter and it read 29.86 HG, which pretty well agreed with the local forecast.
Yet the altimeter reading was -420 feet. Had to crank the dial to get it to field elevation. When I did so, the pressure then read 30.35 HG, which was clearly incorrect.
Maybe I'm losing it, but still think there's a calibration issue.
It's 55 years since I did any serious (military) flying, but I'd like someone to go through the exact same procedure and explain this.
as usual, Best Regards to all.