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I believe that the term declination was used in error in this article. On any nautical navigation chart the difference between magnetic and true north is called “variation.” Declination has always been the angle from the horizon to a point higher into the sky.

Bob Nickelson
King and Queen Court House, Va.

While navigators use the term variation to avoid confusion with declination (which indeed has astronomical meanings), some groups of geologists use declination to describe the angle between true north and magnetic north.