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Jim, you mentioned slide rules.  I don't know about the Bygrave, but
there is a book available on the web, called ``Slide Rule for Sea and
Air Navigation'', by J. C. Podmore, available for download at
http://sliderule.ozmanor.com/man/man-download.html (scroll about 4/5
of the way down the page).

Chapter VI - Dead Reckoning and Astronomical Calculations, mentions
traverse tables, amplitudes, azimuth,prime vertical observations,
errors, dip, parallax, refraction and ex meridians.

That might help you get started using a regular sliderule for some of
this stuff.  The next chapter is on coastal navigation

Nels

On 12/6/05, Jim Hickey  wrote:
>
>
> Alternate methods of sight reduction
>
> First, allow me to introduce myself as a new member. My name is Jim Hickey.
> My wife Judy and I currently live aboard our sailboat in St. Augustine,
> Florida. I have been interested in celestial navigation for many years much
> to the amusement and entertainment of my wife! Even got the programming bug
> early on but have it under reasonable control at this time. It has been a
> delight to read many of the fascinating postings for some time now.
>
> I have a volume of Bowditch that discusses a variety of sight reduction
> methods. I believe all the old table methods and more have been discussed.
> Has anyone had access to or knowledge of the old slide rule type method that
> is referenced? I believe the instrument was called a Bygrave computer which
> looked cylindrical.
>
> As well, there is also a picture of a wonderfully elegant looking globe like
> device that is set up with sliding arms that solves the navigational
> triangle directly.
>
> I have been intrigued by these items for years and of course would love to
> mess with them if I had the chance as I am sure many here would.
>
> Very curious to know how effective these approaches were and if there are
> others etc. etc.
>
> Cheers,
>
> Jim

   

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