And Leroy, where are you suggesting that Mr Freeman put this mu-
metal? If you put it anywhere near the compass you will significantly
alter the compass readings. If it happens that he has a speaker on
his panel (or an instrument that has a speaker built-in) then it is
concievable that encompassing the speaker in mu-metal could be helpful
but that is the only scenario I could see for mu-metal. If he does
have a loudspeaker on the panel, a better solution would be to remote
it.

Brian W is correct that if he happens to have power wiring running
near the compass, then get it away from the compass and twist it with
the return.

Alas, why bother? Compasses are relics with all sorts of annoying
foibles.

Steve