Direction: True, Magnetic, Wind and Compass Errors

Charts are drawn to true north, but your compass points to magnetic north, so you must convert. The angular difference at your location is magnetic variation, shown by isogonic lines: add westerly variation to, or subtract easterly variation from, the true course to get the magnetic course. A further small error, deviation, comes from magnetic influences within the airplane and is corrected with the compass correction card. Wind adds another adjustment: because a crosswind pushes you off course, you turn slightly into it by a wind correction angle so your actual track matches the desired course, and the wind triangle also gives the resulting groundspeed — lower into a headwind, higher with a tailwind. Finally, the magnetic compass itself misbehaves during acceleration and in turns: remember ANDS (Accelerate North, Decelerate South), and expect the compass to lag near north and lead near south. It is trustworthy only in straight-and-level, unaccelerated flight.