You are steering 142°pgc to make good your desired course. The gyro error is 1°E. The variation is 8°W. What should you steer by standard magnetic compass to make good the desired course?
DEVIATION TABLE Magnetic Heading Deviation 120° 4°E 135° 2°E 150° 0
• Relationship between true, gyro, magnetic, and compass headings (T–G–M–C relationships) • Effect of east or west gyro error on converting between true and gyro • Using variation and deviation (and the deviation table) to convert between magnetic and compass headings
• First, work from the gyro course you are steering to find the true course. Ask yourself: with a 1°E gyro error, is the gyro reading higher or lower than true? • From your true course, apply the 8°W variation. Decide: do you add or subtract westerly variation to get magnetic? • Once you have the magnetic heading, use the deviation table around that heading. Do you need to interpolate between two values or can you use one directly? Then decide whether to add or subtract deviation to find the standard magnetic compass course.
• Be clear on the rule: “east error, gyro least; west error, gyro best” and how that changes gyro to true • Confirm you applied 8°W variation correctly when going from true to magnetic (TVMDC sequence) • Make sure the deviation sign (E or W) is applied correctly when going from magnetic to compass, and that you used the proper heading range from the table
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