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    Re: Grads and logical units. Was:[NAV-L] Compass card with more than 360 degrees
    From: Jean-Philippe Planas
    Date: 2006 Apr 7, 12:17 -0700
    For what it's worth French protractors are still graduated with two scales. One in Grades (400 grades in a circle) and in Degrees (360 degrees in a circle).
    The first definition of the kilometre 220 or so years ago was one hundredth of a Grade taken at the earth equator. Thus the earth diametre on the equator is about 40000 km and one grade at this location is 100 km.
    This is very similar to the definition of the nautical mile based on 360 Degrees.

    George Huxtable <george@HUXTABLE.U-NET.COM> wrote:
    | I've lost track a bit of the 400 whatevers around the compass, but you
    | are talking about grads (you'll even find the measurement on some
    | calculators). 400 grads in a circle.
    | We think of the metric system being firmly established in the world, but
    | only a part of it -- measurement of distance and temperature -- is
    | universal.
    | Grads were part of the original metric system, an attempt to make arc
    | measurements more convenient than the 360 degrees inherited from the
    | ancient world (Babylonians?).
    | Interestingly, so was a new time measurement -- the French divided the
    | day into 10 hours, each hour into 100 minutes, each minute into 100
    | seconds. That makes a metric second just a tiny bit smaller than our
    | usual second. Just imagine what metric time would mean for navigators
    | -- no borrow/carry mistakes calculating time intervals!

    Comments from George.

    Grads (100, not 90, to the right-angle) still appear on some French maps. To add to the confusion, I understand that in some
    languages, such as German, grad is their name for the degree, which is not the French Grad.

    The French Grad is not a very logical unit, however. The Turn would be a much better one, with the milliturn being the sub-unit. In
    which case, sextants would be marked up to about 333 mT, not 120 degrees. No minutes and seconds of angle, of course, decimal

    That would fit nicely with time units of a day and a milliday. Breakfast would be about 300 md, lunch 550, dinner 800, bedtime 1000.
    Time would be given by new clocks in which the slower hand made just one turn in the day, not two. No minutes and seconds of time,

    Think how easy that would make navigation calculations, if lat and long, and dec and GHA, were measured in milliturns. Instead of
    the sky moving at (very nearly) 15 degrees per hour, it would move by 1 milliturn in a milliday.

    Of course, all existing clocks, sextants, maps, protractors, would have to be thrown away.

    Well, I can dream, can't I?


    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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