magnetic declination

(redirected from Compass variation)
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Synonyms for magnetic declination

the angle (at a particular location) between magnetic north and true north

References in periodicals archive ?
The idea of this system was to correct for the fact that when sailing on a due westerly compass heading, the course error introduced by compass variation would bring the ship to a different latitude after sailing some distance.
A more reliable method, espoused by Spaniard Pedro de Medina and Frenchman Jean Rotz among others, was to use the observed bearing of the noon-day sun to determine compass variation on the spot, and then use that known value to adjust compass headings.
Within a few decades, chart directions were given in true bearings and navigators were expected to make a correction using a value for compass variation obtained by the navigator from local measurement or from published tables.
The causes of compass variation -- or `Declination' in technical terms -- are still not perfectly understood.
Halley contented himself with more observations of compass variations.