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Solving For Compass Deviation

While proceeding up a channel on a course of 010° T per gyro compass you notice a pair of range lights in alignment with the masts of your vessel when viewed forward. A check on the chart shows the range to be 009° T and the variation on the compass rose to be 15° W. If the ship's course is 026° psc, what is the deviation on the present heading?

SOLUTION:

Have you heard that "true virgin makes dull companion"? We are going to use that mnemonic.

        TRUE = 009°
VARIATION = 15° W
MAGNETIC = 024°
DEVIATION = __?
COMPASS = 026°

As we can see in tabulation above, we have no entry for the deviation. So what value and sign of deviation are we going to add or minus to the magnetic?

Since our magnetic is 024° and our compass is 026°, so we can now understand that the deviation must be 2°. But what will be the sign? In true to compass (uncorrecting), west is to be added. So 2° W will be the deviation.


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