On 17 April your 1610 ZT DR position is LAT...

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Question 1 of 2066636eea28f7522a1c51ab3d

On 17 April your 1610 ZT DR position is LAT 22° 07.0' N, LONG 158° 16.0' W. At that time, you observe the Sun bearing 271° psc. The chronometer reads 03h 08m 52s, and the chronometer error is 01m 16s slow. The variation is 4° E. What is the deviation of the standard magnetic compass?

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Question 1 of 20

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🔍 Key Concepts

• True bearing vs. Compass bearing and how to convert between them using variation and deviation • How to correctly apply chronometer error to get accurate GMT for sight reduction • Relationship between pscd bearing (per standard compass), magnetic bearing, and true bearing

💭 Think About

• From the observed psc bearing, how do you step-by-step get to a true bearing of the Sun using variation and deviation? Or are you instead starting from a computed true bearing and working back to find the unknown deviation? • How does correcting the chronometer time affect the calculated Sun azimuth from the sight reduction tables or calculator? • Once you know the true azimuth of the Sun at that time and position, what is the sequence of corrections (and their signs) to go between True (T), Magnetic (M), and Compass (C) to isolate the deviation?

✅ Before You Answer

• Be clear about the sign convention: East variation/declination is added going from True to Magnetic ("East is least, West is best" helps you remember whether you add or subtract). • Check that you have correctly applied the chronometer error (a slow chronometer means actual GMT is later or earlier?). • Before picking an answer, write out the full conversion chain like T – Var = M; M – Dev = C (or the reverse, depending on direction), then solve algebraically for the unknown deviation and check whether it should be East or West.

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