On 1 September your 1115 zone time DR position is LAT 25°20.0'N, LONG 28°24.0'W. At that time, you observe the Sun bearing 160.5°psc. The chronometer reads 01h 14m 58s, and the chronometer error is 01m 17s fast. The variation is 13.5°W. What is the deviation of the standard compass?
• Converting zone time to UTC (GMT) using chronometer time and error • Using DR position, date, and GMT to obtain the Sun’s true bearing from the Nautical Almanac or sight reduction tables • Relating true bearing, variation, and deviation to a standard compass bearing
• First, think about how to correct the chronometer reading using the given error. Is a chronometer that is “fast” ahead of or behind UTC? • Once you have GMT, how do you use the DR position, date, and time to find the Sun’s true bearing at that moment? Which tables or references would you consult? • After finding the true bearing of the Sun, how do you compare it with the observed standard compass bearing to solve for deviation, knowing the variation is already given?
• Be sure your GMT is correct after applying chronometer error; a sign mistake here will throw off everything. • Confirm you are using the correct convention for west variation (does it make magnetic east or west of true?) before solving for deviation. • When you compute deviation from the relationship between true, magnetic, and compass bearings, double-check the E/W sign with the “east is least, west is best” memory aid.
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