How to Adjust for Declination

March 17, 2014

How-to-Adjust-for-Declination

  • The difference between true north and magnetic north is known as the magnetic declination or variation.
  • If magnetic north is west of true north—as is the case throughout the Northeast—it’s a west declination. If east, then it’s an east declination.
  • To convert from a true bearing (one determined from a map, for example) to a magnetic bearing (what your compass shows), add a west declination or subtract an east declination. 
  • A mnemonic can help keep this straight in your head.
    •  “Empty Sea, Add Water” is shorthand for “MTC, Add W,” which stands for “Map to Compass, Add West.” 
    • “From map to field the proper yield is east is least and west is best.” This phrase translates to: “From true to magnetic, subtract an east declination and add a west declination.” 
  • To convert from magnetic to true, simply reverse the formula.

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Matt Heid

Equipped blogger Matt Heid is AMC's gear guru: He loves gear and he loves using it in the field. While researching several guidebooks, including AMC's Best Backpacking in New England, he has hiked thousands of miles across New England, California, and Alaska, among other wilderness destinations. He also cycles, climbs, and surfs.