magnetic declination

plural magnetic declinations

1. countableuncountableThe horizontal angle between magnetic north and true north at a given place.

   By the 17th century several instruments had been designed to measure the magnetic declination.

   2002, Michael Windelspecht, Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 17th Century, page 149

   2 more examples

   In the Ste Genevieve District, magnetic declination varies significantly within short distances due to iron-rich bedrock, and this might account for magnetic declinations varying from five to ten degrees east in Soulard's surveys.

   2002, Walter A. Schroeder, Opening the Ozarks: A Historical Geography of Missouri's Ste. Genevieve District 1760-1830, footnote, page 159

   This is corrected by setting the magnetic declination of the compass. This is a correction value given on all navigation maps. Once set with the magnetic declination, a compass will point to the true North Pole also known as the “Geographic North Pole." All places on Earth have a slightly different magnetic declination depending on how you line up with both poles. In an extreme case, if you stood between the two poles and faced the real North Pole, your masgnetic compass would point to the magnetic North Pole behind you—a magnetic declination of 180 degrees!

   2005, Phil Medina, Homework Helpers: Earth Science, page 53