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    Re: sextant precision.
    From: Frank Reed CT
    Date: 2005 Jun 19, 21:05 EDT

    The other option (for getting shade error on a dense shade):
    Get a piece  of good welder's glass or equivalent, dark enough to look at the
    Sun straight  on. With no shades down, hold the welder's glass up to your eye
    and look through  the sextant. Because of its location, optical imperfection
    in this glass will  not matter. Now adjust the sextant for an ordinary IC test
    bringing the Sun's  direct and reflected image into limb-to-limb contact.
    Lower the sextant, set  aside the welder's glass, and swing in that dense shade.
    Whatever gap or overlap  is now present between the direct and reflected Sun
    images is due entirely to  the dense shade. Adjust it away and there's your
    shade error.
    
    If you're  worried about holding the welder's glass in front of your eye
    where it might be  heated by the focused light from the sextant's telescope, it
    also works fine if  you hold it directly in front of the objective lense of the
    telescope.
    
    Does that all make sense?
    
    -FER
    42.0N 87.7W, or 41.4N  72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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