What does 'variation' refer to in navigation?

• A. Difference between true and magnetic north
• B. Difference between compass and gyro
• C. Difference between east and west bearings
• D. Difference between magnetic declination and grid north

Answer: (A)

Variation is the angular difference between true north and magnetic north. This difference is what you must account for when using charts oriented to true north alongside a compass that points to magnetic north. The magnetic variation shown on charts tells you how much to adjust bearings to switch between true and magnetic references. If the variation is east, you add it to a true bearing to get the magnetic bearing; if it’s west, you subtract it.

This concept is distinct from deviation, which is the difference between a compass reading and true north caused by the ship or vessel’s magnetic interference (not a map reference). It’s also different from grid north, which is the direction along the grid lines on a map; the difference between magnetic north and grid north is called grid variation. In practice, variation helps you translate directions on your map (true bearings) to what your compass will show (magnetic bearings).