Stiknruda,
Calibration should be quite simple, I hope. Simply stall the aircraft in three configurations -- flaps up, flaps 25 and flaps 50 and note the AoA of each. Then make a best angle and best rate climb and note the AoA of each of those. Then land and mark each of those angles on the AoA indicator with a bit of coloured tape.
It's a very low tech affair, which is why I like it. Rather like the sight level fuel gauges on the Super Cub -- very little ambiguity is possible.
To all the doubters: my reg is G-CUBP. You can look out for it in the AAIB reports.
QDM