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    Re: AN5954 bubble octant by Bausch and Lomb
    From: Gary LaPook
    Date: 2012 May 4, 15:11 -0700
    See if this helps.

    http://fer3.com/arc/imgx/A-6-Octant-Manual.pdf

    "Don't let the perfect be the enemy of the good."

    For use in flight, the median is "good enough" (especially considering the magnitude of the other possible inaccuracies)  and a whole lot easier to derive than the average for a changing altitude. Many octants used this method, A-7, A-10, A-12 and your B&L  and probably others.

    gl

    --- On Fri, 5/4/12, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:

    From: Alexandre E Eremenko <eremenko@math.purdue.edu>
    Subject: [NavList] AN5954 bubble octant by Bausch and Lomb
    To: NavList@fer3.com
    Date: Friday, May 4, 2012, 1:53 PM


    Dear List members,

    Does anyone have this octant or a manual to it?
    I see a picture and a description in Ifland's book.
    Unfortunately this description makes no sense for me:-(

    The main distinction from all other air octants is that
    it is "medianizing" instead of averaging.
    Instead of averaging it takes a median of 15 altitudes,
    with a very simple "medianiser". There is a picture which
    is supposed to show this medianiser in action, and it seems
    clear how it works.

    Let me recall what is the median. You order 15 numbers by their
    magnitude and take the 7-th. This is the median.
    Median has some substantial advantages in comparison with
    the average, if you repeatedly measure the SAME quantity.

    This does not apply however to sextant altitude observatons,
    except for the Polaris and Sun at Noon.
    In general, altitude changes quite quickly and when you take 15 shots,
    the results are very likely to be increasing or desreasing.
    In which case there is evidently no point of taking the median.
    (It will be simply the 7-th shot).

    That's why I am looking for a more reasonable explanation of how this
    sextant really works, or what is it for.

    Alex.




       
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