Search the Web on Mu-Metal. It can provide some improvement. Won't
necessarily remove all interference, but may be enough to swing the
compass. We had to do this in one of our powered aircraft.
Leroy

Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.