Back on to track, My plane had a vertical card compass when I bought it.
I had noticed that it was rather inaccurate, and seemed to wander, eventually it was 160 deg out. I have replaced it with a traditional liquid filled compass. I took the old one apart to find out how they work. This one has a 1 inch diam magnetic disk with a 45 deg chamferred cog wheel on top, the wheel mates with another horizontally mounted cog on a shaft that drives the vertical compass card. It seems that the horizontal shaft was an interference fit into the compass card, and had come loose. It seems to be OK in cold weather but free to turn in hot weather. There may be different makes of these compasses, but there is no way of knowing if your compass suffers the same problem. I would throw it away and replace it with a liquid filled jobby, ok these do occasionally leak, but that is pretty self evident, but spotting that your compass has suddenly swung 20-30 degrees out whilst flying may not be so easy. Pete
