Magnum is almost certainly right, since by definition, compass swings are likely to be carried out at home base anyway.
Compasses are adjusted for Southern or Northern Hemisphere operation and I think that the old ARB rule is still accepted as good-practice. There is an amusing typo in the current Light-Aero Spares catalogue, advertising compasses for "North Hampshire" or "South Hampshire" use, which is a bit too restrictive for me.
G