On 5 September in DR position LAT 23° 17.0' S, LONG 154° 35.0' E, you observe an amplitude of the Sun. The Sun's center is on the visible horizon and bears 275° per standard magnetic compass. The chronometer reads 07h 49m 26s and is 01m 52s fast. Variation in the area is 3° W. What is the deviation of the standard magnetic compass?
• Amplitude of the Sun to find true bearing at the time of observation • Converting between TRUE, MAGNETIC, and COMPASS (T–M–C) using variation and deviation • Correcting chronometer time (fast/slow) to get correct GMT, then LMT, then applying to the Sun’s true azimuth
• How do you use the date, DR longitude, and corrected GMT to find the Sun’s true bearing (true azimuth) at the instant of the amplitude? • Once you have the Sun’s true bearing, how do you step through TRUE → MAGNETIC using the given variation, and then MAGNETIC → COMPASS using an unknown deviation? • Given the observed compass bearing and your computed magnetic bearing, should deviation be labeled East or West for this situation?
• Be sure you have corrected the chronometer time properly for the 01m 52s fast indication before using it. • Confirm the sign and application of variation 3° W (does west variation make magnetic greater or less than true?). • Check that you correctly apply the East/West deviation rule: "Compass best, error West – Compass least, error East" when comparing compass and magnetic.
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