I have briefly unscrewed the cover off my MT102 fluxgate (to inspect something) and upon putting it back I find the heading is 3 degrees greater.
But the screw holes are such that no significant rotation is possible.
All the screws and washers appear stainless steel.
I can just do another compass swing (a 2hr job with a laptop, a precise compass and a load of hassle) but I wonder if I might have magnetised some of the screws by using a screwdriver which is magnetised (as many are, a little bit).
If I have magnetised any screws, re-swinging the compass is not a good solution because presumably they will gradually lose their magnetisation… If this was suspected, I ought to first replace them with brass screws, but brass on aluminium is not great for corrosion reasons.
I can’t see anything which might not be stainless steel, except possibly those nutplates.
