M or B (I can't remember which) resets the heading indicator - sometimes
you have to set it every 15 min. because it replicates the pressision or
whatever you call it that the gyro.. depends on your realism setting but it
could mess up your IFR test if you're heading in the wrong direction, even
though you think you're lined up correctly. The other of course sets your
alitmeter to the correct setting for alt.

ok this isn't making sense but "m" resets the heading indicator to the true
heading (compass heading) so ususally I hit M, and B

hope that made sense,

Matthew