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    Re: Logic of shades
    From: Greg Rudzinski
    Date: 2018 Oct 31, 09:00 -0700

    Alex.

    A 6" slide rule is good enough for almost all navigation needs except for calculated altitude Hc , time sight local hour angle LHA, and great circle distance ZD (zenith distance).

    I use the 6" for time speed distance, azimuth, prime vertical, ex-meridian, amplitude, interpolation, horizontal sextant angle circle of position radius, vertical distance off, dip, refraction, and appx Hc pre calculation.

    For Hc. ,time sight, and great circle distance slide rule calculations I like using the Ottis King with 1' trig tables.

    Greg RudzinskiFrom: Alexander Duytschaever
    Date: 2018 Oct 26, 06:38 -0700

    Hello,

    I'm a n00b user/amateur astronav that dived into astro navigation after stumbling over a Bris sextant and wondering if one could ever perform LOP calculatons using a slide rule (got a few of those) :-) (*) So I soon acquired a small shiny King Hughes 1917 replica and recently a Davis Mk 15, and I can happily live with their shortcomings (found an article on how to deal with those shortcomings, and I still have to calibrate these three).

    My question is: what is the logic behind the different shades? I understand that one needs more shades for the index mirror (4 vs 3 for the horizon), but why were those colours (blue, blue, orange, grey) chosen? I suspect that the light grey colour can be used for moderate lighting or to increase contrast, and it also reminds of lunar light conditions; but the two blue glasses look similar (I guess a main function is to block out UV), but are there intended ways to combine those glasses?

    thx

    -alex-

    (*) for now, my answer is that a SR can serve for interpolations; it doesn't have enough digits to provide sufficient accuracy. or maybe with A LOT of sightings, who knows...

       
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