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    Re: Another sight reduction analog device
    From: Gary LaPook
    Date: 2012 Apr 28, 00:32 -0700
    Basically it projected the Weems Star Altitudes Curves on to a flat surface for plotting. Since the curves were on a roll of film the device tool up a lot less room than the Weems book of curves.

    Both of these methods show that the determination on latitude is independent of time, the two altitude curves will always cross at the same latitude. But that intersection moves around the world at 15° 02.46' per hour so you need time to determine the location of the intersection in longitude. Another way to look at it is that crossing two LOPs provide a fix in latitude and LHA Aries and you then use time and the GHA of Aries to convert it to a longitude value.


    --- On Fri, 4/27/12, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:

    From: Alexandre E Eremenko <eremenko@math.purdue.edu>
    Subject: [NavList] Another sight reduction analog device
    To: NavList@fer3.com
    Date: Friday, April 27, 2012, 6:51 PM

    It is called an Astrohraph,
    and the book by M. D. Wright says:
    "The only mechanical reduction device to achieve wide acceptance
    was the astrograph".

    This it says after discussing the Hagner position finder and
    citing Weems's opinion on it which more or less coincides with my opinion
    of such devices which I stated in my previous message, except that I
    tried to be more polite than Weems:-)

    Few pages earlier the book however says on Bygrave rule,
    that "two Britain's most famous navigators, Chichester and D. Bennett
    relied on Bygrave rule", they mean Chichester as an airplane navigator,
    of course.

    Now I recall that astrographs were also mentiones in Soviet navigation
    books (Marine navigation!).


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