On 17 April your 1516 zone time DR position is LAT 27°24.0'N, LONG 115°24.0'E. At that time, you observe the Sun bearing 247°psc. The chronometer reads 07h 16m 26s, and the chronometer error is 00m 32s slow. The variation is 4.5°E. What is the deviation of the standard compass?
• Using an azimuth of the Sun to determine compass error • Relationship between true bearing, magnetic bearing, compass bearing, variation, and deviation • Correcting a chronometer time with known error to obtain the right UTC for sight reduction
• How do you turn the observed 247°psc bearing of the Sun into a true bearing step by step? Think about what corrections (if any) apply between compass and true. • Once you compute the Sun’s true azimuth from your DR position and UTC, how do you compare that to your observed bearing to get total compass error? • After you know total compass error, how do you separate it into variation and deviation to isolate the deviation of the standard compass?
• Be sure you converted chronometer time + error into the correct UTC before entering the Nautical Almanac or sight reduction tables. • Check that you have the correct sign convention: is easterly variation added or subtracted when going from true to magnetic, and from magnetic to compass? • After finding total compass error, carefully apply the known 4.5°E variation (with the correct sign) to solve for deviation, then match its size and east/west sense to one of the choices.
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