The angular difference between true north and magnetic north; indicated on charts by isogonic lines is called what?

The angular difference between true north and magnetic north; indicated on charts by isogonic lines is called what?

• A. Variation
• B. Deviation
• C. Magnetic Declination
• D. True North

Answer: (A)

The main idea is magnetic variation. The angle between true north and magnetic north at a location is called variation, and charts show lines of equal variation called isogonic lines. Knowing the variation lets you convert between true headings and magnetic headings when plotting courses. Deviation is different: it’s the local error of the aircraft’s compass caused by magnetic interference inside the airplane, not something shown by isogonic lines. True north is simply the geographic north direction and isn’t describing this angular offset. Magnetic declination is another term some use for the same concept, but aviation charts routinely refer to it as variation, which is why this choice fits the described concept.

The main idea is magnetic variation. The angle between true north and magnetic north at a location is called variation, and charts show lines of equal variation called isogonic lines. Knowing the variation lets you convert between true headings and magnetic headings when plotting courses.

Deviation is different: it’s the local error of the aircraft’s compass caused by magnetic interference inside the airplane, not something shown by isogonic lines. True north is simply the geographic north direction and isn’t describing this angular offset. Magnetic declination is another term some use for the same concept, but aviation charts routinely refer to it as variation, which is why this choice fits the described concept.