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    Re: 4-digit Circular Sliderules
    From: Hanno Ix
    Date: 2015 Apr 20, 17:00 -0700

    I have completed six versions of the 4-digit cricular sliderule I reported about in February - two of 12", two of 10" and two of 8" diameter. Each pair incorporates the two schemes of finding the proper turn on the 20 turn spiral as I presented there. On the backs I put the haversine table, the hav-Doniol fomula, plus example.

    On the 8" version this table is readable if you have crisp vision and strong light - not always the case. So I replaced it with my azimuth diagram which has been described several times on this list. Out came a very nice combination which should make it useful for an expanded number of CelNav problems beyond hav-Doniol sight reduction.

    All versions' results for multiplication and division are exact within 4 digits as desired. These SR is easy to operate and to read, and the color scheme is very helpful. The 12" is particular fun to work.

    There are 2 pointers as in all circular SR. Here, one is a transparent disk of the same diameter as the scale and has a black line. The other is a transparent 1" strip with a red line. Typically, the disk is made out of clear plastic, however there is one type of plastic sheet you can write on notes with pencil and erase them again. The slight penalty is less transparency. This is version is actually my personal preference.

    Designing/plotting the scales was the simple part! Once I had the plots printed by Kinko (great job!) , I had them attached to a hard foam sheet by a shop that makes signs. Making an accurate pivot, however, is easy only if you have a lathe which I do. The difficulty was to make the friction adjustable, and adjustable with only one tool: a penny. You know, special tools might get lost on board! Also, making narrow, crisp and durable lines turned into a challenge. SHARPIE pens just wouldn't do the job well enough. I ended up with threads glued on with clear Scotch tape, but finding a procedure for this that works accurately and repeatably took me some time. I he am happy with the result.

    Just to make it clear, these SR are not intended for sale. However, if some one wishes to build his copy I will give practical advise as much as I can.



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