TVMDC

TVMDC is a method for converting true, magnetic and compass headings. TVMDC is expressed as: True, variation, magnetic, deviation, compass. The most common use of the TVMDC method is correcting courses during nautical navigation.

Background

The Geographic North Pole and the Magnetic North Pole are not exactly the same position on the earth. From any position on the globe, a direction can be determined to either the geographic north pole or to the magnetic north pole. These directions are expressed in degrees from 0-360, and also fractions of a degree. The difference between these two directions is known as variation. While a compass is installed in a vehicle or vessel, local anomalies of the vessel can introduce error into the direction that the compass points. The difference between the direction to Magnetic North Pole and the direction that the compass is pointing is known as Deviation.

Determine variation in North America