On 27 June your 1905 ZT DR position is LAT 24° 35.0' N, LONG 50° 15.0' W. At that time, you observe Saturn bearing 211° pgc. The chronometer reads 10h 04m 26s and the chronometer error is 01m 20s slow. The variation is 4.5° E. What is the gyro error?
• Relationship between true bearing, magnetic bearing, and gyro bearing including the roles of variation and deviation • How to convert between chronometer time and Greenwich Hour Angle (GHA) of a body using chronometer error • How to compare the computed true bearing of Saturn from the DR position with the observed pgc (per gyro compass) bearing to find gyro error
• From the DR position, date, and time (with chronometer error applied), what is the true azimuth (true bearing) of Saturn you would compute from the Nautical Almanac and sight reduction tables? • Once you have the true bearing of Saturn, how do you step-by-step move between true, magnetic, and gyro bearings, using the given variation, to see which way the gyro must be in error? • Is the gyro reading too far to the east or to the west compared with the true bearing, and by how many degrees?
• Be sure you apply chronometer error (slow) correctly when finding the correct GMT for the sight • Keep track of the algebraic sign of variation (4.5° E) when converting between true and magnetic • When you compare the calculated true/gyro bearings, check carefully whether the resulting gyro error should be labeled East or West
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