Which statement is true about magnetic deviation of a compass?

Magnetic deviation refers to the errors in a magnetic compass reading caused by local magnetic fields generated by the aircraft itself, such as electrical equipment and metal structures. As such, deviation is specific to the individual aircraft and can change depending on its heading due to the orientation of magnetic influences inside the aircraft.

When an aircraft turns, the magnetic fields affecting the compass can be different depending on its direction. For example, a piece of equipment that disrupts the magnetic field on one heading may not do so on another, resulting in different compass readings as the aircraft turns. This means that a pilot can experience varying compass readings at different headings while flying the same aircraft, which is why this statement about deviation being influenced by different headings in the same aircraft is accurate.

In contrast, the other options suggest constant or varying behavior of deviation that doesn't account for the compass's dependence on the aircraft's heading.