To receive accurate indications during flight from a heading indicator, the instrument must be...
A. set prior to flight on a known heading.
B. periodically realigned with the magnetic compass as the gyro precesses.
C. adequately powered so that it seks the proper direction.
B. "You should check the heading indicator against the magnetic compass at least every 15 minutes, and more often if the instrument is showing signs of age such as grinding noises or rapid precession" (3-10)
Note: do this only at straight-and-level flight, or else the compass will probably be off.
(this multiple choice question has been scrambled)