Compass Deviation Calculator
Convert between true, magnetic, and compass headings
Input Heading
°
Corrections
Heading Conversion
Compass Heading
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True Heading
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Magnetic Heading
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Compass Heading
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Total Correction
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TVMDC Memory Aid
True Virgins Make Dull Companions
T → V → M → D → C
True + Variation = Magnetic
Magnetic + Deviation = Compass
West is Best, East is Least
Going True → Compass: Add West
Going Compass → True: Add East
Variation vs Deviation
Variation
Difference between true and magnetic north. Caused by Earth's magnetic field. Found on nautical charts in the compass rose. Changes slowly over time and varies by location.
Deviation
Compass error caused by magnetic influences on your specific boat. Varies with heading. Should be checked annually by swinging the compass. Recorded on a deviation card.