Your vessel is proceeding up a channel, and you see a pair of range lights that are in line ahead. The chart indicates that the direction of this pair of lights is 186°T, and the variation is 11°W. If the heading of your vessel at the time of the sighting is 193° per standard magnetic compass, what is the correct deviation?
Official USCG Answer & Rule Citation
Correct Answer: Option D — 4°E
Range lights provide a known True direction (186°T). Applying easterly or westerly variation (11°W) yields magnetic heading (197°M). Comparing magnetic heading with standard compass heading (193°psc) using the rule 'Compass least, Easterly best' establishes a deviation of 4°E.
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