In reply to FesteringSore:
> I loaded a digital compass app on to my phone. I was quite amazed at how inaccurate they can be when compared with a standard magnetic (Silva) compass. Despite following the instructions for calibration there is, at times, a discrepancy of up to 60 or 70 degrees.
How did you test the phone compass against the Silva compass?
If you had the Silva compass near the phone when you compared them the magnets in the phone speakers would affect it but (hopefully!) the phone's digital compass would be calibrated to compensate for them.
I guess the digital compass in a phone is mainly to give GPS a hint about which way you are facing so as to orient the map display and there's not much reason to put effort in to make it super accurate. Not many people are going to want to take bearings when they have a GPS.