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    Re: Newbie - Variation Question
    From: George Huxtable
    Date: 2002 Feb 13, 23:31 +0000

    My last message crossed with the latest postings from Yves Arrouye and Dave
    Weilacher.
    
    Let me try to simplify the discussion by defining exactly what is observed
    on this instrument, the GPS receiver by the French firm MLR Electronique,
    type SP24 and also SP24Y. The firm is now owned by Thales Navigation.
    
    First, set up a waypoint at the North Pole and from anywhere on Earth,
    observe what the receiver gives as the magnetic course to that waypoint.
    
    If the "compass var." setting on the instrument (or in French, "deviation
    compas") is at zero degrees (as is originally preset when you take it new
    out of its box), then as you would expect, the magnetic course to that
    waypoint is zero degrees.
    
    Now if you change "compass var." to 10W (the sign is set as E or W, not +
    or -) the indicated compass course to the North pole waypoint becomes
    350deg, not 10 deg as it should be. The only way to obtain the correct
    magnetic course that you need (010 deg.) is to take the variation given on
    a chart (say 10 deg West) and enter it as "10E".
    
    There's no need to go into what you add or subtract from what to get what.
    The behaviour is clearly WRONG. There is a serious blunder in the
    programming of that instrument, which will result in magnetic courses in
    error by twice the variation. As far as I can tell, the makers are
    attempting to deny the blunder (as I have found out in discussion with
    their distributor). I have emailed M.  L. Moreau at
    lmoreau{at}thalesnavigation.com and await his reply.
    
    The manual is completely silent on this matter, except for the following words-
    "BRG = Bearing from your position to the position of the destination
    waypoint, in degrees. This bearing relates to true North but an off-set to
    compensate for local compass variation may be entered if required."
    
    Taken with the label "compass var.", would the user expect to enter against
    that label the compass variation from the chart, or a variation in the
    opposite sense?
    
    I think the maker's attitude is dangerous, and makes matters worse. Once a
    user has been alerted to the problem, the danger largely vanishes. But if a
    user, ignorant of the problem, tries to set magnetic courses, he is likely
    to find himself in considerable danger.
    
    I intend to publicise the matter, and wonder if any listmember can advise
    me about other navigation mailing lists which do not exclude electronic
    navigation, and how to join so as to post an appropriate warning message.
    
    George Huxtable.
    
    
    ------------------------------
    
    george---.u-net.com
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.
    ------------------------------
    
    
    

       
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