Originally Posted By: Russ
I thought that was magnetic deviation.

ETA: Magnetic declination is synonymous with variation.


I was taught that magnetic variation was due to the difference in magnetic and true north, and that changes with location not the vessel, while magnetic deviation is due to a vessel's own structure and magnetism.

For merchant mariners, Bowditch has always been the "Bible." See Chapter 6: http://www.irbs.com/bowditch/pdf/chapt06.pdf