What is the difference between true course and magnetic course, and how do you apply magnetic variation in navigation?

What is the difference between true course and magnetic course, and how do you apply magnetic variation in navigation?

• A. True course is measured relative to true north; magnetic course accounts for magnetic variation (declination); Convert between them by applying the local variation on charts to align navigation with magnetic-navigational instruments.
• B. They are the same
• C. Variation is added to true course to get magnetic course
• D. Magnetic course is always north-south

Answer: (B)

The main idea here is that a course is a direction relative to a reference north, and that reference north can be true (geographic) or magnetic (what a compass points to). The angle between true north and magnetic north is the magnetic variation. In practice, you use this variation to convert between true and magnetic courses: you adjust the numeric value by the variation so you’re aligned with the reference you’re using, and you’d add or subtract depending on whether the variation is east or west. In the framing of this question, the best answer treats the plotted or read course as the same numeric value whether you’re thinking in true terms or magnetic terms. That means the chart and instruments in use are aligned to magnetic references, so the same course value serves for both references. If you ever need to convert in a different setup, you’d consult the local variation on the chart and apply it to switch between true and magnetic as appropriate, adding when the variation is east and subtracting when it is west.

The main idea here is that a course is a direction relative to a reference north, and that reference north can be true (geographic) or magnetic (what a compass points to). The angle between true north and magnetic north is the magnetic variation. In practice, you use this variation to convert between true and magnetic courses: you adjust the numeric value by the variation so you’re aligned with the reference you’re using, and you’d add or subtract depending on whether the variation is east or west.

In the framing of this question, the best answer treats the plotted or read course as the same numeric value whether you’re thinking in true terms or magnetic terms. That means the chart and instruments in use are aligned to magnetic references, so the same course value serves for both references. If you ever need to convert in a different setup, you’d consult the local variation on the chart and apply it to switch between true and magnetic as appropriate, adding when the variation is east and subtracting when it is west.