Definition
The card carries the graduations, historically in points of 11.25 degrees and now in degrees from 000 to 359, and is attached to the magnet assembly so it stays aligned with the field while the vessel turns about it. The lubber line is the fixed reference on the bowl, which must be aligned precisely with the fore and aft line; any misalignment introduces a constant error on every heading that will be misread as deviation.
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