Compass Errors

[PhotoPilot]

After doing a bit of ground with a few of my students, I'm curious as to the flying community's knowledge relating to our trusty mag compasses. I'll start with a poll and hopefully let that garner a few responses before the discussion starts.

Ready? Here it is:

 

[PhotoPilot]

And, for the 8 people who answered, the answer is no. The compass does NOT have a counterweight, contrary to what Jeppesen and about a million other sources say. I have no idea where this particular aviation myth started, but man is it pervasive! Almost every one of my new Instrument students thought there was some little bit of metal strapped to the southern pole of the compass in the plane.

Magnetic dip is countered by the low CG of the compass card (pivot high, bar mags low). The acceleration and turning errors are accounted for entirely by the residual effects of dip, as can be neatly demonstrated with a paper cup and a knowledgeable demonstrator. The counterweight is a figment of the imagination . . .