Flinders bar

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A Flinders bar is a vertical soft iron magnet placed in a tube on the fore side of a compass binnacle. The Flinders bar is used to counteract the vertical magnetism inherent within a ship and is usually calibrated as part of the process known as swinging the compass where deviations caused by this inherent magnetism are negated by the use of horizontal (or quadrantal) correctors.

Where the deviation from a compass point cannot be counteracted through the use of magnets, a deviation card, or graph, is produced. This card, or graph, lists the deviation for various compass courses and is referred to by the navigator when compass courses need to be corrected.

Named after Matthew Flinders (1774-1814).