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    Re: Using a slide rule for celnav
    From: Gary LaPook
    Date: 2014 Jan 21, 00:19 -0800
    Good question. I only became interested in it after reading Chichester's book about crossing the Tasman Sea in 1931 utilizing the Bygrave to find tow small "must find" islands along the way. (I have this book on my computer and can send it to anybody who wants a copy, it is a great read.)
    I don't know how much they cost and then there is the problem with them loosing the friction between the cylinders necessary to keep them from sliding after being set. Those of us who have made copies of the cylindrical Bygrave know how difficult it is to get everything right. Fortunately, it is a lot easier with the Flat Bygrave. ( https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule ) The Germans made a lot of their copies and used them on ships and submarines and they included a locking mechanism for the tubes.

    gl




    From: Francis Upchurch <francisupchurch---.com>
    To: garylapook---.net
    Sent: Monday, January 20, 2014 11:23 PM
    Subject: [NavList] Re: Using a slide rule for celnav


    I use a homemade replica Bygrave for most of my LOPs, great circles and the second half of my lunar clearances (still can't do the first bit!see earlier postings. Any maths wizards please help!). Generally get within 1' of a calculator result and nearly as quick. I use a replica cylindrical Fuller for general cosine formulae and the lunar first bit (cosine formula). The Fuller is twice the size of the Byrave with vulnerable brass cursers and I've nearly finished a miniaturized version (similar size to Bygrave),with robust curser that is just as accurate (albeit with the aid of magnifying glasses to see the reduced scales.)This gives 4-7 decimal place accuracy with any formulae but a bit slower than the Bygrave.I've never tried using a 10" linear for cel nav. Very interested to hear it works better with Bygrave formulae.I will now try the mini Fuller using the Bygrave formulae. From what Gary has been saying, this may be even more accurate?
    I can send details in a couple of weeks on request.
    Another unanswered question, perhaps to Gary? The Bygrave is faster and just as accurate as Air Almanac in my experience, second only to modern calculators. why was it never standard issue during WW2? Only a few top RAF navigators used it and Chichester does not mention it in his RAF nav instruction books.
    Francis
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