On 10 June your vessel's 0519 zone time DR position is LAT 27°07.0'N, LONG 92°10.0'W, when an amplitude of the Sun is observed. The Sun's center is on the visible horizon and bears 063.6° per standard magnetic compass. The variation in the area is 4.8°E. The chronometer reads 11h 17m 32s and is 01m 18s slow. What is the deviation of the compass?
• Amplitude of the Sun for finding compass error (difference between true bearing and compass bearing at the horizon) • Converting standard compass bearing → magnetic → true using deviation and variation relationships • Determining whether deviation is E or W from the order: True–Magnetic–Compass ("T V M D C")
• From the date, time, and DR position, what is the Sun’s true bearing at the moment it is on the visible horizon? Think about how you’d get this from the Nautical Almanac and sight reduction tables. • Once you have the true bearing, how do you step through True → Magnetic → Compass, and where does variation fit into that chain? • When compass reads higher or lower than true, how do you decide if deviation is labeled E or W?
• Make sure you correct the chronometer time properly using the stated error (slow/fast) before entering the almanac. • Apply the local zone description correctly to relate zone time to UTC/GMT before extracting Sun data. • When solving for deviation, double‑check the sign convention: Easterly corrections are added, westerly corrections are subtracted in the T–V–M–D–C sequence.
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