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    Re: Time of meridian passage accuracy
    From: Gary LaPook
    Date: 2009 Sep 28, 10:18 -0700

    George commented about my post about the usefulness of the traditional
    noon sight:
    
    "Gary has omitted the most important reason why it was historically so
    useful. It didn't call for any knowledge of time."
    
    
    Well, you do need a calender :-)
    
    gl
    
    
    
    
    George Huxtable wrote:
    > Gary wrote-
    >
    > "There is nothing magic or special about an LOP taken at noon. It is only
    > due to its simple computation that made it useful in the past to navigators
    > without the necessary math skills to do the trig for a Sumner line of for
    > the St. Hilaire method that gave it any usefulness."
    >
    > Gary has omitted the most important reason why it was historically so
    > useful. It didn't call for any knowledge of time.
    >
    > "Since the normal use of these tables allow you to choose an AP within 30 NM
    > of the DR this allows a 4 minute period that you use the tabulated Hc, two
    > minutes to the east and two minutes to the west. So certainly using the time
    > to one one minute falls into the normal level of accuracy for celnav LOPs."
    >
    > Gary is referring to the normal use of an observation at LAN for determining
    > latitude. There is, indeed, much leeway in timing that observation, just as
    > he says.
    >
    > But Bowditch, rather unexpectedly, read "To calculate latitude AND LONGITUDE
    > at LAN, the navigator seldom requires the time of meridian passage to
    > accuracies greater than one minute." It's in calculating longitude from
    > around local apparent noon that a much better time of the moment of noon
    > than to the nearest minute is called for.
    >
    > George.
    >
    >
    > contact George Huxtable, at  george{at}hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    >
    >
    > >
    >
    >
    
    
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