Is the compass mirror usable outside North America?
 

I'd like to replace my dimming interior mirror with the version that includes a compass, but all the calibration data is only given for North America.

So if I buy one from e.g. vagparts.com how will I know the correct calibration value to use in the UK?

Yes, you need only convert your local magnetic variation into a number the mirror can use. I'd
 

suggest using the map of N.A. as a guide.

I thought magnetic variation only accounted for ~10 degrees variance?
 

Since the compass is only accurate to 45 degrees, I wouldn't think it would make any difference practically. You'll always know you're in the correct quadrant, you'll just be wrong on which half of it you're in, about 1/4 of the time.

WTF are you talking about?

Magnetic north pole is not the same as the true north pole. Error on east coast is about 9 degrees

Welcome back, Jim - where ya been? We've missed you.

Right, and out here it's 20 degrees, but having a compass that
 

compensates for it should result in accurate readings, even at magvars > 10 degrees, as proposed by AvramD. The variation in Alaska is upwards of 40 degrees, but my compass still works there if properly calibrated.