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    Bubble sextant index error
    From: Michael Dorl
    Date: 2005 Dec 10, 13:06 -0600

    So, how do I determine the index error of my bubble sextant without a water
    horizon?
    
    Maybe stand half way between my house and my neighbors house (200 meters
    between them) and establish a mark on each house at the same level per the
    bubble.  Any departure from horizontal in the bubble will be the same for
    both sights.  Then walk over to my house, place the sextant at the height
    of the mark and measure the elevation of the other mark.  One minute at 200
    meters equals 1 * 2 * PI * 200 /(360 * 60) = 0.06 meters = 2 inches; don't
    think I'll be able to make that kind of distinction.  The parallax
    introduced by the displacement of the prism and the direct view is of that
    order.  Doubt if I can do much better than 3 or 4 minutes.
    
    
    

       
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