How is magnetic variation expressed?

Magnetic variation, also known as magnetic declination, is expressed in degrees east or west of true north. This measurement is crucial for navigation, particularly in aviation, because it indicates the difference between true north (the direction of the North Pole) and magnetic north (the direction a magnetic compass points).

Understanding magnetic variation is essential for pilots and navigators as it affects how they interpret compass readings and adjust their flight paths. For instance, if a navigator is aware of the magnetic variation for a specific area, they can accurately convert their compass headings to true headings, ensuring that they maintain their intended route.

The other options do not pertain to magnetic variation. Altitude is a vertical measurement, meters above sea level is a unit of measuring elevation, and nautical miles relate to distance traveled over water, none of which align with the concept of magnetic variation.