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Subject: Re: Newbie - Variation Question
From: Yves Arrouye (yves@XXX.XXX)
Date: Wed Feb 13 2002 - 00:29:24 EST
> 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
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