Definition
Produced by swinging the compass, the card lists deviation, named East or West, at intervals of typically 10, 15 or 45 degrees of ship's head, often with a smooth curve fitted through the values. It is dated, signed by the compass adjuster, and posted near the steering position. It must be redetermined after any structural work, engine change, new electronic installation, a lightning strike or a long period in one berth, and periodically as permanent magnetism decays.
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