To convert true heading to magnetic heading, you need to do what with the variation?

To convert true heading to magnetic heading, you need to account for magnetic variation, which is the difference between true north and magnetic north. Variation can be either easterly or westerly, depending on your geographic location. When the variation is easterly, it means that magnetic north is to the east of true north, which is often the case in certain areas. This means that to convert true heading to magnetic heading, you would subtract the easterly variation, as you are effectively moving westward along the arc of a circle to realign to magnetic north.

Conversely, when the variation is westerly, magnetic north is to the west of true north, and therefore you would add the westerly variation to the true heading to find the magnetic heading. The correct approach encompasses both situations, indicating that you subtract easterly variation or add westerly variation as needed. This captures the accurate adjustment required for the conversion to magnetic heading.