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    Re: Margetts' 1790 Longitude Tables
    From: Francis Upchurch
    Date: 2018 Jan 26, 23:03 -0800

    I love these and made a copy on an A3 printer which is much more accurate then the small A4 . I agree with everything Frank says, but the shear beauty of the thing is a wonder.A sort of graphical artistic analogue computer 1790. I get pretty good results now in about 3-4 minutes. I prefer pictures to log tables where I tend to make even more mistakes and take 20  minutes plus. (The 1790 methods of clearance would have probably taken longer?)

    The other wonder is that someone managed to make a perfect digital copy of a rare survivor, put it on the internet and enable me and probably others to re-create this 200 years later. 

    See the Navlist post by Ken Muldrew, 26th April 2006. He suggested possible ways these were made originally. Even with graphical interpolation between individual points, this must have involved hundreds of the lengthy ,log based calculations available in the 1780s and then expert engraving of 100 plus plates. Some job! No wonder they were expensive.

    Apologies for the blured photos. I'll try to get better ones if anyone wants them.

    Francis



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