Don’t think there is an adjustment. Is this an A0 or A1?
On an A0 which uses old school electric resistance transducers there are a pair of transducers under the left dash in front of your left shin when seated. real easy to get to if you pull out the STE connector and bracket(About 5 minutes and 2 connectors).
Each transducer has 2 conections, one for the pressure sense to the gauge and one to the pressure sw that drives the low air buzzer.
The first test I would do would be to swap the sensor wires from one transducer to the other. The Pressure sense wires are Tl150 and TL151. Swapping these two will connect the rear transducer to the front gauge and vis-versa. If the same gauge reads low, then the gauge is the issue. If the problem moves to the other gauge when you swap the wires, the transducer is. You could also do this swap by lifting the dash and swapping the gauge plugs between front and rear.
The newer integrated panels on the A1/A1R use a data bus to provide info to the gauges and an integrated gauge controller that has the pressure transducers soldered to its mainboard inside the box. I have heard of one person replacing a bad pressure transducer in one of these boxes, so they can be worked on…
