What do the inner rings on a compass rose on a chart indicate?

The inner rings on a compass rose on a chart represent magnetic degrees and the variation between magnetic north and true north. This is essential for navigational purposes, as it helps mariners understand how to adjust their headings based on local magnetic variations.

The magnetic compass does not point directly to true north due to magnetic declination, which is the angle difference between magnetic north and true north. The inner rings provide a reference for mariners to convert between magnetic bearings (the direction the compass points) and true bearings (the direction relative to the North Pole).

Ultimately, these inner rings are crucial for any navigation involving a compass, ensuring that the vessels maintain the correct course by compensating for local magnetic influences. Understanding how to read these rings is a fundamental skill for effective navigation at sea.