When transitioning from a compass course to a true course, what should be applied?

The transition from a compass course to a true course requires consideration of both variation and deviation to ensure accurate navigation.

Variation, also known as magnetic declination, refers to the difference between true north (the direction of the geographic North Pole) and magnetic north (the direction a magnetic compass points). This difference can vary depending on your geographical location and must be applied to convert a compass course to a true course effectively.

Deviation, on the other hand, is the error introduced in a compass reading due to local magnetic fields, such as those created by metal objects or electrical equipment on a vessel. It is essential to know the deviation for a specific compass to adjust the reading accurately.

Applying both variation and deviation gives a navigator the exact true course, which is crucial for plotting a safe and accurate course over the ground in navigation. The need to account for both factors reflects the complexities of using magnetic compasses in conjunction with the Earth's magnetic and geographic reference points, making the combination of both the correct and necessary step in this transition.