On May 20, 12:33 am, John Godwin wrote:
"Ken S. Tucker" wrote in news:a15da157-a236-
:

Well duh, it's a magnetic compass in a fluid.

While flying in IMC, I had a compass seal fail 10 miles from my
destination ... gawd, smelly compass fluid all over the cockpit.

When thought through, the Mag-Comp is quite the
precision instrument. That fluid needs be able to
not freeze down to what, maybe -40F. (Ron from
Alaska might know). It also sits in an Arizona sun
and can't expand to burst, though yours (John)
may have.
It also has a viscosity that keeps the thing from
gyrating all over the place, the one we used had
a slow lag while banking, so if you wanted to come
to 180 level the wings for 178 and the thing creeps
to 180.
Ken