Which statement about the Flinders bar of the magnetic compass is CORRECT?

Correct Answer: Option C — It compensates for the error caused by the vertical component of the Earth's magnetic field.

The Flinders bar is a vertical soft-iron rod placed near the magnetic compass to compensate for the vertical component of the Earth's magnetic field. As a vessel changes latitude, the vertical intensity of the Earth's field changes, and the Flinders bar corrects the resulting deviation, as detailed in Bowditch, Chapter 6.