What’s the difference between compass bearings and true bearings?

Magnetic vs True Directions

A navigation compass indicates magnetic direction, which is the direction a magnetic needle aligns itself with. On the other hand, true direction refers to the actual direction to a location, considering the Earth’s magnetic field and any magnetic declination in the area. Magnetic declination is the difference between magnetic and true directions, usually measured in degrees.

To navigate effectively, it’s essential to understand the difference between magnetic and true directions. In most regions, magnetic declination ranges from 5 to 20 degrees, but it can be as high as 30 degrees in some areas. For example, in North America, the magnetic declination is around 10-20 degrees east of true north in the United States and Canada, but can vary significantly in Alaska and other areas. A navigator must consider this declination to avoid making errors in navigation.

Using a Compass Correctly

To determine true direction, a navigator must add or subtract the magnetic declination from the magnetic bearing. For instance, if the magnetic bearing is 30 degrees, and the magnetic declination is 10 degrees east, the true bearing would be 40 degrees. Conversely, if the true bearing is 40 degrees, and the magnetic declination is 10 degrees west, the magnetic bearing would be 30 degrees. By accounting for the magnetic declination, a navigator can ensure accurate navigation and avoid getting lost.