Entering a harbor, you take a bearing on a range and get 338° per gyrocompass (pgc). The true bearing from the chart is 340°T. Variation for the area is 14°E. Your course is 329° per standard magnetic compass (psc) and 338°pgc. What is the deviation on this heading?
• Gyro error and how to find it from true vs. gyro bearings • The TVMDC relationship: True, Variation, Magnetic, Deviation, Compass • How east/west errors (variation and deviation) affect the sequence when converting between True, Magnetic, and Compass
• First, compare the charted true bearing with the gyro bearing to determine the gyro error and its east/west sense. • Next, use True and Variation to find the Magnetic direction; then relate that to the standard magnetic compass heading given. • Finally, decide whether the compass is east or west of magnetic on this heading and by how many degrees.
• Confirm the sign convention in TVMDC (does east variation/deviation make compass higher or lower than true?). • Verify the arithmetic when going from 340°T with 14°E variation to get the equivalent magnetic direction. • Compare the resulting magnetic direction with 329° per standard compass and determine if the compass reads high or low relative to magnetic on this heading.
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