Compass in mirror not accurate

[skidooboy3]

I have a 2004 Trailblazer with the electrochromatic mirror with compass built in. When I got it, the compass only would read "NE" or "NW". I doublechecked that the zone was correct and it was. I also reset it to calibrate itself again and now it gives some different readings occasionally but mainly sticks on two or three directions. Does anyone know if this is a problem in the mirror or in a sensor somewhere and what's the best way to figure out what's causing it. Thanks.

[maxwedge]

Mine does this also, especially in some areas where the power lines cross the road,.

[mdtpr]

my 02 loves the SW only direction for some reason even if I'm going NE.