I haven't felt a need to use a hand bearing compass for many years
(pre-radar).

Today I needed to take a bearing on a location ashore, from my boat. The
radar was off and I pulled out my old Richie from the locker. I had brought
it over from my last boat and had inherited it from that boats previous
owner. Never really use it or looked it over.

When I took my bearing, it was obvious that it was off by over 45 degrees.
Took the bearing several times, check the way I was operating the compass
card hold/release button, etc.

Went to the work bench and opened the case (two screws). Ah Ha! The (at
least) 10 year old illumination batteries were still in it. Very corroded,
but this was confined to the battery contacts.

Corroded batteries shouldn't cause a bearing error, however while replacing
the batteries I noted a label that required that the batteries be "Non
Magnetic". Gave two mfg'ers part numbers. The batteries I had onboard
turned out to have a dramatic effect on the compass, as did the old ones.

So, not only had I neglected to service the hand bearing compass batteries,
but I (or the previous owner) had installed magnetic batteries.

Sure glad I wasn't taking critical bearing that could have put my boat on
the rocks.

Until I can locate a source for these special Non Magnetic batteries, I will
operate it without illumination. (once the compass card is locked, I can use
a flash lite to read the bearing.)

--
My experience and opinion, FWIW

Steve
s/v Good Intentions