In order to check your compasses, you sight North Dumpling Island Light in line with Latimer Reef Light bearing 077°pgc. The helmsman was steering 307°pgc and 320° per standard magnetic compass at the time. Which statement is TRUE?
• Gyro error: Relationship between true bearing, gyro bearing, and whether the error is east or west • Compass error and deviation: How to move between true, magnetic, and compass using variation and deviation • Use of a chart range (two lights in line) to get the true bearing of the range from the chart
• On the chart, draw a line through North Dumpling Island Light and Latimer Reef Light. What is the true bearing of that line, and how does it compare with the observed 077° per gyro? • Given the helmsman steered 307° per gyro and 320° per standard magnetic, what does that difference tell you about the relationship between the two compasses? • Once you know gyro error from the range, how can you use the local magnetic variation to separate magnetic compass error into variation and deviation?
• Be sure you correctly identify the true bearing of the range from the chart before comparing to 077°pgc. • Keep the sign convention straight: for gyro, remember how True, Gyro, and Gyro Error relate when the error is east vs west. • Before deciding on any statement about deviation, confirm the local magnetic variation in that area and apply the "west is best, east is least" memory aid correctly.
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