Thx for the feedback. No, the question is like its mentioned. There is nowhere an a\c type or heavy\light a\c,...
And you are right, found also some interesting stuff in inet:
Link:
http://www.cfinotebook.net/notebook/...scopic-systems
With this in mind, the correct answers are:
Magnetic compass and CDI
And I was always so sure that the magn. Compass is definitely affected but that much that it could be adversely affected (only a few degrees but still working), but I think this is the reason why the authorities use these words. Only to trick you around and make you doubting your thoughts, even when they are right.