At 1538 ZT on 15 October, in DR position LAT...

Question 1 of 2707066636eea28f7522a1c51aafb

At 1538 ZT on 15 October, in DR position LAT 18° 12.8' S, LONG 160° 48.4' E, you observe an amplitude of the Moon. The center of the Moon is on the visible horizon and bears 276.2° psc. Variation is 10° E. What is the deviation?

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Question 1 of 27070

🔍 Key Concepts

• Amplitude of the Moon and how it is used to check compass error • Relationship between true bearing, variation, deviation, and compass bearing (TVMDC) • Effect of east or west variation and deviation on converting between true and compass values

💭 Think About

• From the observed amplitude, what true bearing of the Moon should you expect at that latitude and time of year? Think about whether the Moon should be north or south of the east-west line. • Start with the observed compass bearing and work step-by-step through variation and deviation: in which order do you apply them, and with what signs? • Once you find the total compass error, how do you separate that into known variation and unknown deviation?

✅ Before You Answer

• Be clear about psc (per steering compass) vs. true bearing – do not mix them. • Confirm you are using the correct sign convention: east is usually least, west is best, depending on which way you are converting. • Double-check whether the resulting deviation should be labeled E or W based on whether the compass points too far east or too far west of true.