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Re: Newbie - Variation Question
From: Yves Arrouye
Date: 2002 Feb 12, 21:29 -0800
From: Yves Arrouye
Date: 2002 Feb 12, 21:29 -0800
> That is the way the french deal with variation (declinaison) > > The basic formula being: > True + Variation = Magnetic > > They consider : > West variation as positive and > East variation as negative > > So the negative East variation is added to True to get the Magnetic. Difference between France and Quebec? ;-) I learned Cv = Cc + W (True = Magnetic + Variation) W positive if East W negative if W Fromn that one finds Cc = Cv - W so that would say subtract too. (Le Cours de Navigation des Glenans, 1990, says "if the variation is East, it is substracted from the true heading". Also, when taking sightings, the sentence "Est-ce Plus ou Est-ce Moins (Est Plus, Ouest Moins)" is used to go from magnetic to true.) It is the first time I hear about East variation being considered negative, but this all arithmetic, right? Add the negative quantity, or substract the positive one, who cares? If Andrew's GPS let him enter "15 E" for the variation, then his magnetic headings should be 15 degrees less than the true heading (doesn't this GPS come with a manual? What does it say?). If he entered "+15" thinking that this means "15 E" then Pierre's explanation justifies it. Pierre, any pointers to texts that refer to the variation as negative if East? All I can find says through a quick France Google pages says it's positive if East. YA