What does magnetic compass deviation represent?

Magnetic compass deviation refers specifically to the variations in the compass reading caused by local magnetic fields within the vessel, influencing the compass. Traditionally, the term "deviation" describes how a magnetic compass may not point to true magnetic north due to interference from metallic structures or electronic equipment onboard.

The answer highlighting that deviation is the angular difference between magnetic north and compass north accurately reflects this interpretation. While the compass aims to point towards magnetic north, the presence of nearby magnetic influences can lead it to deviate from that intended course. Understanding this concept is crucial for navigators, as it helps them account for the discrepancies in compass readings when plotting courses or determining headings.

In this context, other options do not represent deviation correctly. For instance, while it is true that compass readings can vary based on the bearing being used—taking into account the magnetic influences at that specific heading—this does not define deviation in its fundamental sense. Also, deviation is not directly published on compass roses on nautical charts; that publication typically relates to variation, which is different from deviation. Lastly, the distinction between geographic and magnetic meridians is relevant to magnetic variation, not deviation. Thus, acknowledging deviation as the angular difference between what a compass shows and what it should show is key