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Compass Variation and Deviation (TVMDC question)

Last Updated: Dec 29, 2016 09:16AM EST

A question on the compass quiz states:

To find a magnetic compass course from a true course you must apply:

  1. Deviation and Variation
  2. Deviation
  3. Variation
  4. Magnetic anomalies

I answered Variation by applying the TVMDC principle. it was wrong. The correct answer was Variation and Deviation. Why would deviation come into play? The difference in magnetic and true is variation. Only if you were figuring PSC would you need deviation.

Using the TVMDC principle is the correct method for solving this problem. 

However, you must recognize that Magnetic Compass goes in the (C) Compass portion of the TVMDC table not the (M) Magnetic. Remember that for the purposes of this course all compasses are magnetic. With this knowledge when the question refers to a magnetic compass and you apply the TVMDC formula you should now be able to see that Variation and Deviation must be applied when you find a MAGNETIC compass course from a TRUE course
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