Compass course

Compass course is the ship’s intended track measured clockwise from compass north, the direction the magnetic compass card actually indicates. It differs from magnetic course by deviation and from true course by compass error. To convert, apply error with the rule correct from compass to true by adding easterly error and subtracting westerly: true equals compass plus easterly compass error. The navigator steers a compass course but lays the track on the chart in true, so every helm order referenced to the magnetic compass passes through the deviation card and the local variation before it becomes a charted course.