NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Newbie - Variation Question
From: George Huxtable
Date: 2002 Feb 13, 23:31 +0000
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@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@huxtable.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------