compass
Hi Pete:
I think you'll find that locating a compass in the panel can lead to large errors. It might be possible to find a location that has minimal magnetic deviation, but it may be sensitive to electric currents from adjacent wires or instruments. You won't know until it's too late to change.
I have the type that mounts to the windscreen support. I chose the location by using a handheld compass, and finding the point that had the least deviation. For a bunch of reasons, the steel in the roll bar and support are slightly magnetized, and it's best to find the neutral point before installation.
When I swung the compass, I ended up with a maximum 1 degree of error throughout 360 degrees... which is probably as good as I could align the aircraft on the compass rose. The Dynon EDC and the compass agree to within 2 degrees.
Vern Little
Final inspection complete - no snags. As soon as the interim C of A is issued, I can fly.