Variation refers to which condition?

• A. Compass error caused by the difference between magnetic north and geographic north.
• B. An error in heading due to wind drift.
• C. The angular difference between true north and magnetic north at a location.
• D. A local interference effect near power lines.

Answer: (A)

Variation is the compass error caused by the difference between magnetic north and geographic (true) north. A magnetic compass points toward magnetic north, but navigation often uses true headings based on geographic north, so the two directions don’t align exactly at any location. The angle between them is shown as magnetic variation on charts and must be accounted for when converting between true and magnetic headings. For example, if variation is east, magnetic north lies east of true north, so you add variation when going from true to magnetic, and subtract it when going from magnetic to true. This concept is distinct from wind drift, which is caused by crosswinds, or local interference (deviation) inside the aircraft that affects the compass reading.