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    Re: Navigator's Slide Rule
    From: David Pike
    Date: 2020 Aug 18, 14:59 -0700


    They look very nice and obviously took a lot of hard work.  Have you tried the red and black one under red light as might be encountered in a warship operations room or aircraft cockpit? I use red light at night to try and save my night vision. The light level at most navigation stations including yachts must be subdued at night so as not to spoil your night vision when you do look out or use the sextant.  Seeing small detail is always a struggle requiring rapid changes between reading and distance glasses if you’ve less than perfect vision.

    I’ve done a bit of experimenting.  Red on a flat surface like maps hardly shows, but the odd red figures on my high-school green and white CASTELL slide rule show black under red light.  I think it must be because of the depth of the engraving.  Mind you, black on black wouldn’t be much good either. 

    Bomber Command did some interesting work on which colours show up best to indicate what you might see of the ground at night from in a darkened cockpit.  Try googling ‘bomber command pilots target map’ in Google Images.  They finally settled on the grey and purple ones.  DaveP



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