A compass can be invaluable for navigation, and should be part of a larger toolkit consisting of a topographic map, watch, altimeter, and GPS. In the first of two videos on using a compass, Sierra Designs brand ambassador and National Geographic “Adventurer of the Year” Andrew Skurka explains two basic skills: how to adjust for declination and how to orient a map.

The magnetic needle in a compass does not point in the direction of True North (towards the geographic North Pole), but in the direction of Magnetic North. The angular difference between the direction of True North and Magnetic North is known as declination. In the continental United States, the current difference can be as large as 16 degrees, which would be a significant error if not adjusted for properly. Declination changes slowly over time, due to the movement of molten iron within the Earth’s outer core, which gives the Earth its magnetic field.

Once you know how to adjust for declination with your compass, the first operation you should learn is orienting a map. When your map is oriented, the features on the map align perfectly with the features in the field. This is a very useful technique when, for example, you are at a trail junction, or when you are looking out across a landscape trying to identify peaks and valleys.