Some systems display the direction ahead at the top of the screen, instead
of North. This makes it so North is at the top only when you are actually
going North. This setting is usually User Adjustable.
I have a 05 525iAT. My systems even works in tunnels and when turning in
underground garages. That's why I beleive there is an accelerometer
involved. Might also be supported by a magnetometer.
GPS can determine direction, but not as fast as a magnetometer or an
I recently fitted a Mk1 sat nav system to my e38 and it seems to use a
combination of road speed, an electronic compass and the GPS to work
out where it's going. I don't actually have the compass (magnetic
probe) fitted to mine and it does get a bit confused sometimes. I
*think* all systems use the compass.
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