Compass placement adjacent to GPS unit?

If the GPS unit has a speaker in it it will have a magnet and yes that will affect the compass as would any circuit in the unit that has a reasonable amount of current flowing through it, or any Ferris metal in any objects located close to the compass.

To be safe would be to test bench it and see what affect there is on the compass, most good compasses will have correction adjustments inbuilt but they can only correct for minor magnetic disturbances.

Cheers
Leigh

Calibration and adjustment can be tricky Bungarra.

Some thing that works is to stand behind the car away from metal at least a metre and note which way the needle is pointing - carry unit into car and move around to possible mounting places and check that needle still points to same direction.

In practise a small deviation is ok as most compasses and peoples use of them is only for general direction anyway.

Interesting to note is that often starting the car will cause a flick of the needle but it will probably settle in about same direction.

A magnets in speakers, an interactive GPS and also power in cable can all put a compass off. Safer and easier to move it away.

Phil