In the previous lessons you learned to calculate the Magnetic Variation and also to find out the Magnetic Deviation by using the Deviation Card.

Let’s assume that the True Course plotted on the chart is 020 degrees, the Variation is 3 degrees West and the Deviation is 5 degrees East.

To find out the Magnetic Course, proceed as follows;

Firstly calculate your Magnetic Course using the formula: True to Magnetic – add Westerly Variation and subtract Easterly.

In our case 020 degrees True plus 3 degrees (West) equals 023 degrees Magnetic.

Now apply the Deviation to your Magnetic Course using the formula: Magnetic to Compass subtract Easterly Deviation and add Westerly deviation.

In our case 023 degrees Magnetic minus 5 degrees Deviation equal 018 degrees Compass.

The True Course, then, is 020 degrees, and the Compass Course you have to steer is 018 degrees.

Follow the same method if you want to convert a True Bearing to a Compass Bearing.