You need to make 225°M. Using this deviation card, what course do you steer by the ship's compass?
A ship's deviation card listed by magnetic heading. Heading 180°: deviation 1°E. Heading 225°: deviation 3°E. Heading 270°: deviation 4°E. Heading 315°: deviation 2°E.
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222°C. Going from magnetic to compass works the same way as true to magnetic: subtract easterly deviation, add westerly. The card shows 3°E on this heading, so steer 222°C. Deviation changes with the boat's heading, which is why it comes as a card.
