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    Re: Gunther Rules for Navigation
    From: Brad Morris
    Date: 2017 Apr 20, 12:45 -0400

    I note that all of the scales claimed by Bowditch are present on the rule you presented

    S-R.      Sine Rhumbs 
    T-R.      Tangent Rhumbs
    Num     Logarithmic Scale of numbers
    Tan       Tangents
    Sin        Sine
    V-S       Versed Sine 
    Mer      Meridional Parts
    EPa      Equal Parts

    The scales on the bottom might be

    Cho       Chords 
    Sin.        Sine of minutes?
    Tan.       Tan of minutes?
    ST.          Sine and Tangents of small numbers?

    This Gunter's rule appears fairly unused, and might very well be another example of what every navigator "must have" in his kit, but in practice, never used.  The tables in his Epitome were far superior and at least an order of magnitude more accurate, leading to it sitting in the box, unused.  

    The order of magnitude is an estimate, based upon the number of digits we can expect of a slide rule (3), and a typical 6 place table.  The ability to interpolate the tables in the Epitome and extract precise values would be better in accuracy than any value pulled off of a Gunter's rule.


    On Apr 19, 2017 11:20 PM, "Noell Wilson" <NoReply_Wilson@fer3.com> wrote:

    Hi Ed
    Please see: http://www.sliderules.info/collection/nonstandard/023-gunter.htm

    The Gunter rule seemed to be in a state of change and was apparently copied by others. I'd guess that each step was claimed to be "improved". The claimed main improvement was that the Gunter scale could be used like a slide rule instead of having to use log tables.
    I had a hard time reading the rule in your photos but the rule in the example above seems to be fairly comprehensive - except for the errors found in the scales. :-(
    They apparently had the necessary nav functions of a modern slide rule plus an hour to degree conversion scale. Many seemed to be two feet long so accuracy possibly could have been somewhat better than a new-ish 10" slide rule.

    I suspect that there were some errors made on a rolling, candlelit, ship.
    Regards, Noell

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