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    Re: The Noon Fix
    From: George Huxtable
    Date: 2009 Apr 9, 00:23 +0100

    Thank you, Jim. I have your 1985 paper in an ION CD, so that solves the
    problem. If anyone else would like to see it, contact me.
    
    But you didn't answer my question about the sextant correction, and how you
    could know, in advance, what it was going to need resetting to, before the
    time interval was known. That's still puzzling me.
    
    You wrote- " I didn't explore much at the extremes of Latitude and, as you
    have pointed out, there are some where the Sun is never visible. So, the
    method does have its limitations.".
    
    I wasn't (intentionally) pointing to latitudes where the Sun is never
    visible. Just to higher latitudes where the Sun is lower in the sky, so
    changes in altitude, and in the slope of altitude are much less and changing
    more slowly, making determination of the moment of the turnover point that
    much more difficult.
    
    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.
    ----- Original Message -----
    From: "James N Wilson" 
    To: 
    Sent: Wednesday, April 08, 2009 7:19 PM
    Subject: [NavList 7878] Re: The Noon Fix
    
    
    | George:
    |
    | I have wrestled with this problem, and only reluctantly called the
    | position determination by the method a fix. Longitude is determined at
    | noon, but it is based on data taken before and after noon. It is not a
    | running fix, since no lines of position are advanced or retarded. Or even
    | determined. I do discuss a bit the error sensitivity, but not as
    | completely is in the reference, my 1985 Navigation paper.
    |
    | I originally calculated Dhs at two different times bracketing LAN, thus
    | allowing for the different slope of the adjusted hs vs WT line. I
    | abandoned that in the interest of simplicity. For the example I used,
    | that made LAN eight seconds earlier. I considered that was not worth the
    | extra effort, considering other errors.
    |
    | I didn't explore much at the extremes of Latitude and, as you have
    | pointed out, there are some where the Sun is never visible. So, the
    | method does have its limitations.
    |
    | Thanks for your proper critique. As for the details of the arguments,
    | there's not much more in the two and a half page book. It was not
    | intended to be a treatise, but a description of a backup method. The
    | resultant surprise benefits were thoroughly examined to be sure that they
    | were true, but that's the extent of the effort.
    |
    | Jim Wilson
    | ____________________________________________________________
    | Click here for great custom garage plans!
    |
     
    | |
    |
    
    
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