Heading: true → compass

The number you steer on the compass is not your true track. Three corrections sit between the track you want and the heading you fly, added in turn:

compass heading = true track + WCA + variation + deviation

• Wind (WCA). Wind pushes you sideways, so you angle into it. The wind correction angle is how far you crab to hold the track (wind from the right, crab right).
• Variation. True and magnetic north aren't in the same place. Variation is the angle between them, and it changes with location. When magnetic north lies west of true north the heading reads larger, so you add it (east variation, subtract).
• Deviation. The metal and electrics in the aircraft tug the compass needle slightly off. Deviation is that small leftover error, listed per heading on the compass card, and you apply it the same way.

Keep variation and deviation signed, West +, East −, and the whole chain is one addition. Remember the sign with "east least, west best" (memory aid, not in the CARs/TC AIM). Stop after variation and you have the magnetic heading; add deviation and you have the compass heading.

Trap: apply variation the wrong way and you double the error instead of cancelling it; report the magnetic heading when the compass heading was asked (or the reverse); forget deviation and you finish a couple degrees off.

Practice