On 31 May your vessel's 1420 zone time DR position is LAT 29°06'N, LONG 120°06'W, when an azimuth of the Sun is observed. The bearing of the Sun per standard magnetic compass was 255.3°. The chronometer time of the observation is 10h 17m 24s. The chronometer error is 02m 32s slow. The variation for this area is 12.9°E. What is the deviation of the standard magnetic compass?
Official USCG Answer & Rule Citation
Correct Answer: Option B — 2.5°W
Calculate GMT from chronometer data and evaluate the Sun's position using the Nautical Almanac. Solve the navigational triangle per Bowditch sight reduction methods to find true bearing. Apply variation (12.9°E) to true bearing to find magnetic heading, then compare with compass bearing to find 2.5°W deviation.
100% Free & Open Access — No daily limits, paywalls, or gated answers on BrightMariner.