For a while magnetic variation puzzled me because it was said to vary by year and across a map but I had no idea of knowing what it was. Now using features in the Mirage 2000C I have some answers. They might vary from accepted wisdom because the default map year is now 2016 (it used to be 2008?)
1. Yes, it varies by year. At Creech (NTTR map) in 2016 it is -12 in 2016, -13.7 in 2001.
2. Yes it varies across the map, most notably in the South Atlantic - 15.7 off the coast of Chile, -2.2 off Stanley
2016 figures from roughly map centre:
NTTR -12
Caucasus -7.2
PGulf -2.1
Marianas -0.8
Syria -4.9
South Atlantic West -15 East -2.2
Attention @Alpenwolf