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    Re: Prism levels to correct sextant tilt.
    From: Geoffrey Kolbe
    Date: 1999 Nov 02, 12:10 AM

    >However it seems to me that if a ray splitting prism were mounted in front of
    >the horizon glass, it could be used to image the horizon from two sideways
    >directions, say 90 deg apart,   two superimposed horizons would now appear in
    >the index glass. These images would separate as the sextant was rocked and
    only
    >coincide if the sextant were exactly vertical. The image of the sun etc would
    >then be superimposed on these merged horizons in the normal way but
    without the
    >need to rock the sextant during the observation.
    >I don't know if this is what you had in mind or if this idea has been
    exploited
    >anywhere.
    
    Thankyou for the above Clive.
    
    This is pretty much what I had in mind and the idea has been exploited.
    Celestaire used to sell such a prism, which clipped onto the left hand side
    of the horizon glass. They might still do, I have not looked at their
    catalog recently. The claim was that verticality to 0.5 degrees was easily
    achievable using this device, which cost around $40 ten years ago.
    
    Geoffrey Kolbe.
    

       
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