On 6 November your vessel's 0706 zone time DR position is LAT 25° 30.0' N, LONG 85° 35.0' W, when an azimuth of the Sun is observed. The chronometer time of the sight is 01h 03m 30s, and the Sun is bearing 114.0° pgc. The chronometer error is 02m 30s slow, and the variation in the area is 2° W. What is the gyro error?
• Using a Sun azimuth to determine gyro error • Relationship between true bearing, magnetic bearing, and gyro bearing • Correcting chronometer time to get GMT/UT for sight data
• How do you turn the chronometer reading and its error into the correct time to use with your DR position to get the Sun’s true azimuth? • Once you have the Sun’s true azimuth, how do you compare that with the observed pgc bearing to find whether gyro is high or low? • Think about the sign of variation and the order of applying corrections when going from true to magnetic, and from gyro to true.
• Be sure you are using the correct GMT/UT for 6 November when entering the almanac or sight reduction tables • Double‑check the direction of variation (2° W) and remember the correct rule for applying it • Carefully decide whether the gyro compass is reading ahead (east) or behind (west) of the true bearing based on your calculated true azimuth and the observed pgc bearing
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