So I bought a glider with an S-NAV&GPS-NAV not long ago, and I don't really know how to use either. However, when I start up the S-NAV, the unit thinks I am at 28300ft, when actual elevation is 434ft. Obviously, it won't let me adjust the altimeter enough to get the right elevation. On the startup "altimeter" screen, I set the pressure setting to the same as my regular altimeter (29.92 or whatever), but the altitude readout is still way off. Anyone run into this? Is it broken, or am I missing a setting somewhere?