The compass deviation changes as the vessel changes what?

The compass deviation refers to the error introduced in a vessel's magnetic compass reading due to local magnetic fields and influences rather than the Earth's magnetic field itself. This error fluctuates as the heading of the vessel changes because different headings can amplify or diminish the magnetic forces acting on the compass. As a vessel turns, various iron and metallic components within the vessel, or external magnetic influences, can affect the compass needle’s accuracy, causing it to point away from true magnetic north.

While geographical position, speed, and longitude can impact navigation, they do not directly cause changes in the compass deviation. The compass deviation is specifically linked to how the vessel is oriented, or its heading, relative to magnetic influences. Thus, the correct answer emphasizes the relationship between heading and deviation, highlighting the necessity for mariners to be aware of how their heading can alter compass readings.