🔍 Key Concepts
• 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
💭 Think About
• 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?
✅ Before You Answer
• 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.