Originally Posted by craftycoder
Some magnetometers can be calibrated for nearby iron masses, while others cannot. Those that can are generally more expensive (by several times). The $50-60 models do not. If I pick one up, I'll report my real world experience. If the magnetometer is parked up on the bars with the phone and it works then it will be a great feature for those interested in the cost. If it doesn't work, I doubt anyone including myself would have interest paying $300 for a compass that works when you aren't moving.
I typed all this out a few hours ago, and lost it, so i'll try again now that i'm calm... :)
If the placement does affect the reading by x degrees, then perhaps the two most ineffectual positions would be on a top box or the tip of a windscreen. I don't know the size of one of these pickups, but maybe a wire running down the edges of the windscreen.... Both of which are inconvenient in their own reasons....