At 1444 ZT on 28 July, in DR position LAT 40° 56.8' N, LONG 167° 12.4' E, you observe an amplitude of the Moon. The upper limb of the Moon is on the visible horizon and bears 299.3° psc. The variation is 1° E. What is the deviation?
• Amplitude of the Moon (using upper limb on the visible horizon) • Relationship between true bearing, variation, deviation, and compass error • How to convert a prime vertical amplitude problem into a compass deviation problem
• From the DR latitude and the Moon’s declination (from the almanac for 28 July, 1444 ZT), what should the true amplitude be when the Moon is on the visible horizon? • How do you get from the Moon’s observed bearing in psc to true bearing using variation and (unknown) deviation? • Once you have both the calculated true amplitude and the true bearing derived from the compass observation, how do you use their difference to find compass error, and then separate that into variation and deviation?
• Be sure you are using the correct sign convention for variation (1° E) and for deviation (E vs W) when relating them to compass error. • Confirm that the observed bearing 299.3° psc is correctly interpreted as compass and then adjusted step‑by‑step to magnetic and then true. • Double‑check whether the Moon’s upper limb and visible horizon require any specific tab corrections in your amplitude method or tables.
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