My compass went berserk after using a magnetic tank bag. I tried riding around in figure of eights to no effect. I then tried to recalibrate it with a magnet which failed. I gave up and kept riding the bike. A couple of days later it started to work again.
As for the display the display letter (s) tell you your direction of travel plus or minus 45° and the arrow indicates north. I think that the compass may help if you were completely lost.