what??? That is NOwhere near I ever read!
I remember using a 7 degree variance on a compass when in the boy scouts!
it might have been 17!
The variance varies depending on location. Each USGS topographic map gives the variance for the center of that map.
Well, both poles are moving towards the equator, and the magnetic field is weakening. They have been 'on the move' for a long time, and like many other forces of nature, are slow, but relentless.
Pretty soon you may have to use a 180 degree variance (or just paint new N, S labels on your compass).