SPX 5 wheelpilot effect on compass

[Blue Fox]

I mounted a new raymarine SPX 5 wheelpilot on my boat. Works fine, but ... my compass in the binnacle has now a deviaton of 20 degrees! When I lift the compass from the binnacle the deviation disappears. Only thing that has changed is the new wheelpilot. My old simrad pilot (roughly in the same place) certainly had no influence on the compass.
Anybody a similar experience? Is it possible to compensate a compass with this much deviation?

 

[johnalison]

It is possible to correct quite large errors, and I once corrected 14 degrees after fitting a bracket in the wrong place, but it is not ideal and I wouldn't be surprised if the error varied in your arrangement with the angle of heel. The simplest solution might be to put a steering compass on the bulkhead facing you. However, a lot of boats have binnacle/autopilot combinations so I expect someone will have experience of this problem.