Bob wrote:

Regarding the compass heading that shows in the glass displays:


The heading information from the PFD comes from a directional gyro. The
directional gyro's drift is constantly corrected (slaved) by a magnetic
compass located in the tailcone on the airplane. The output of this compass
is electrically "enhanced" and amplified through a "flux gate".

Bottom line: A very accurate, stable, compass reading that never needs
adjustment.

--
Dallas