Does Compass Declination Change Over Time?

Magnetic Declination Change

Magnetic declination, also known as compass variation, is the difference between magnetic north and true north. It’s essential to note that declination rates can change over time due to the Earth’s slightly ellipsoidal shape and the movement of the Earth’s magnetic poles. The declination rate can vary from as little as 0.1 degrees per year to as much as 5 degrees per year, depending on the location.

Measuring Declination Change

Declination change can be measured in various ways, including using declination charts or maps, observing the declination change over time using a compass, or using digital tools such as the National Geophysical Data Center’s (NGDC) declination database. It’s crucial to update your knowledge of declination change regularly, as declination rates can change significantly over short periods. For example, the city of Boston, Massachusetts, has an average declination change rate of about 1.5 degrees per year.

Updating Compass Declination

To update your compass declination, you can use the following steps: (1) Identify your current location’s declination using a declination chart or map, and note the current declination value. (2) Note the declination value for the destination location. (3) Calculate the difference between the current declination and the destination declination, and adjust your compass accordingly. For example, if the current declination is +10 degrees and the destination declination is -15 degrees, you would need to adjust your compass by 25 degrees to get a true bearing.