On 6 November your 0752 zone time DR position is LAT 25° 11.0' N, LONG 76° 07.0' W. At that time, you observe the Sun bearing 119° psc. The chronometer reads 12h 53m 07s, and the chronometer error is 01m 19s fast. The variation is 3° W. What is the deviation of the standard magnetic compass?
• Compass deviation is the difference between magnetic heading and compass heading • Relationship between true bearing, variation, magnetic bearing, and deviation (TVMDC) • How to correct chronometer time and convert zone time to GMT (UTC) for a sight
• First, think about how to get the true azimuth of the Sun at the time and DR position given. What data do you need from the Nautical Almanac? • Once you have a true azimuth, how do you compare it to the observed compass bearing (119° psc) to find total compass error? • After you find total compass error, how does the known variation (3° W) help you separate that into variation and deviation to get the deviation of the standard magnetic compass?
• Be sure you corrected the chronometer time using the given error (fast/slow) before entering the Almanac • Confirm that you computed the Local Hour Angle (LHA) of the Sun correctly using GHA and longitude sign conventions • Use the TVMDC relationship in the correct direction: check whether you are converting from true to compass or compass to true before solving for deviation
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