Andrea Aime a écrit :
> Funny, never knew such a unit existed.
I believe that it is used almost only in France. Grade was the logical
consequence of the definition of "metre", since the historical definition was "1
metre = 1/10000000 of the distance from Equator to North Pole along (forget
which one) meridian". So by this definition, 1 grade = 100 km on Earth.
Navigators use "nautical miles" (1852 metres) instead of "ordinary" miles or
kilometers because of their convenient relationship with minutes of angle: 1/60
degrees = 1 nautical mile. The "grade" was defined together with "metre" as an
attempt to replace this convenient relationship by a metric equivalent: 1/100
grade = 1 kilometre. It got some adoption in the country where the metric system
was born (France), but not much outside as far as I know.
Martin
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