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    Accuracies and real life
    From: Doug Royer
    Date: 2003 Mar 18, 11:44 -0800

    Mr. Hebard and all,allow me to explain my position.What I was trying to
    convey was that accuracy is relative to what the observer wants or needs at
    a certain time.In the case of finding your position at your home I can
    understand the need or want to get as close to the GPS coordinates for
    experimental or personal satifaction needs.My writeing was slanted in the
    direction of what I usualy need.I beleive what you guys are doing and trying
    to accomplish is wonderfull.If through hard work,dilagence in technique and
    practice you can get consistant results = GPS coordinates so much the better
    for all of us.You will then be able to pass that knowlege along to everyone
    else.Please don't let my writing dissuade you from that goal as it isn't
    written in that vein.
    As Mr. Kenchington pointed out in my Horizontal angle bit I wrote
    yesterday,I was a little slim on the explaination.I wished to convey the
    basic idea.He took it from there.Also,on vessels I serve on one usually
    doesn't use a sextant for horizontal angles or vertical angles but uses a
    stadimeter.His detailed explaination of the horizontal angle is correct.
    As for the pots won the largest I can recall was on a voyage from S.F. to
    Singapore in 1994 for $1800.00.I was then a 3rd officer and my main duties
    weren't navigation.It was actually won by an Able Bodied Seaman of the nav.
    watch who was very close to the actual pos. of the vessel(I can't remember
    how close).Most of the time now I'm not even allowed by the master,and
    rightly so, to participate in the evolutions because my main responsibility
    is the navigation of the vessel and  I have a better fix on the position
    than most others on board.Over the course of the transit,some lasting weeks
    with a number of stops in port, the accumulated errors can,without
    dilagence, be substantial to the end position at the time when the evolution
    is halted.I'll estimate 60 % of the time the final positions are < or = 0.4
    nm of the actual position of the vessel. 48 % < or = 0.2nm and 2 % < or =
    Also,on these vessels there is more than GPS to find the pos.Most vessels
    also have Inertial navigation equipment.We will also use any hyperbolic aids
    such as Omega,Delta,Loran where available.All these aids are checked against
    each other constantly to determine that all  nav. systems are functioning
    correctly.It is also worth noting that each of these aids never have the
    exact coordinates that the other systems show.They are all close to each
    other but never exact.

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