On 12 June at 0919 zone time, your position is LAT 26°52'N, LONG 84°34'W. The chronometer reads 03h 17m 00s. Chronometer error is 01m 40s slow. At that time, an azimuth of the Sun is obtained. The bearing is 089.5° per standard magnetic compass. Variation for this area is 4.5°E. What is the deviation of the standard magnetic compass?
• Chronometer correction and GMT – using zone description to convert zone time to GMT and applying chronometer error • Using a Sun azimuth table/computation to find the true bearing (true azimuth) of the Sun at the given time and position • The relationship: True (T) → Magnetic (M) → Compass (C) and how variation and deviation fit into that sequence
• How do you turn 0919 zone time into the correct GMT to enter the azimuth tables, given the chronometer reading and error? • Once you have the true azimuth (true bearing) of the Sun, what is the total compass error, and how is that related to variation and deviation? • When T, V, M, and D don’t all have the same sign, how can you keep track of them systematically so you don’t mix up east and west errors?
• Double-check the chronometer error application (a slow chronometer means what adjustment to the reading?) • Confirm you are using the correct zone description (ZD) sign when converting zone time to GMT for a west longitude • After finding total error (difference between true bearing and compass bearing), be sure you apply variation (4.5°E) with the correct sign convention to isolate deviation
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