A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Alexander Duytschaever
Date: 2018 Oct 26, 06:38 -0700
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?
(*) 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...