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    Re: Coastal Plotting Sheets
    From: Bill B
    Date: 2007 Apr 01, 19:19 -0400

    George Wrote:
    > Yes, to fix by horizontal sextant angles you need to have three marks on
    > shore, and in the right sort of geometrical alignment to give a good cut
    > between the circles, as against only two marks for compass bearings. But in
    > terms of the precision of the result, there's really no contest.
    I'm in full agreement, assuming the objects are carefully chosen.
    Regarding variation and deviation, I go online at the beginning of the
    season and obtain mid-season variation and update the compass roses on my
    charts as well as areas I frequently visit.
    I have found my hockey-puck compass, in almost all circumstances to exhibit
    no noticeable deviation if I pick a spot on a sailboat (usually coaming)
    away from metal or electrical wiring).
    With three objects onshore I take sextant angles between them, and a compass
    bearing to the middle object.  If I draw a line from the center object with
    that bearing corrected to true, and then the observed angles from that
    center line through the objects, I have immediate feedback if my compass
    bearing is off a bit--and in which direction--as the lines from the left and
    right objects will not intersect the center line at the same point.
    This method is of course limited by the precision and accuracy of the
    plotting devices/protractor, but I am constantly amazed at the proximity of
    the plot to the GPS position.
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