Compass Error - Variation + Deviation

Convert compass course to true course using variation (chart) and deviation (deviation card) - the classical "True Virgins Make Dull Company" chain.

CompassDeviationVariation

Compass coursedegDeviation (E +)degVariation (E +)deg

Magnetic course: 47.0°M

True course: 42.0°T

Changing the inputs requires JavaScript. The calculator above shows its default inputs and result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

T = C + D + V

Symbol	Meaning	Unit
$C$	Compass course	°C
$D$	Deviation	°E or W
$V$	Variation	°E or W

Source: Bowditch Pub.9 Ch.6

In short

Convert compass course to true course using variation (chart) and deviation (deviation card) - the classical \

Learn the theory Marine Voyage Planning and Routing