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    Re: Emergency Navigation Was: Black boxes in navigation Now:
    From: Örjan Sandström
    Date: 2012 Jul 14, 16:50 -0700

    Greg, nice work, will likely make something similar.
    I think you have to remake that wheeler with new numbers, polaris current declination is close to 89°18'
    atached is a table I made summer 2010.
    table is part of creditcard sized card, perhaps could be called "emergency creditcard".
    together with other tables (dip, refraction, star declinations...)
    stuff from NA, Burch, Bowditch, Bennet, Kolbe, Crowley, Lagan...
    I even crammed in a basic sun and star almanac
    with some careful fiddling I managed to get a pair of basic starcharts showing n and S poles together with acrux, gacrux hadar cochab, polaris dubhe alkaid alioth in something like their proper positions

    on the dividing, I am a trained instrumentmaker so I have dome things like this countless times, 30' with paper and pencil is ok precision.
    I made one 122mm diam down to 3° and got about with of pencil line precision.


    few hints on getting better results.
    Try using something harder than paper (I prefer Aluminium, brass, bronze or possibly Lexan or Plexi-glass), paper is too unstable and points tend to dig in unevenly and in a non repeatable manner.
    Use finer point than a pencil for the lines, I prefer a stiff machinist divider or a bar divider with one side a needle point and other a knife point (angled scalpel like blade, some models actually use razorblades for points).
    One must be careful to hold divider perpendicular to surface or it tends to dig in unevenly producing elipses and ovals.
    take your time seting up each arc, slightest mistake will repeat and get magnified, in otherwords check and recheck each setting and position s of points before scribing
    use loupe or magnifier to centre pivot needle.
    have good light falling from minimum 3 angles.
    Move head from side to side when setting point it helps in spotting if things are out.
    Use mirrors mirrors to get light in tight places and/or to see point from different directions to help centre, plasticine or wax are good to hold small mirrors when doing this.
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