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    Re: Sextant calibration (arc error)
    From: Bill B
    Date: 2005 May 14, 23:57 -0500

    Frank
    
    Agreed, if sextant parallax error is not a significant factor.  My guess for
    7/8/full-sized sextant-parallax-error average would be 0.1' at 1 nm.  3 arc
    seconds at 2 nm.
    
    Please let me know how you experiments turned out compared to star-to-star.
    
    Bill
    
    > I experimented with a method for testing arc  error last week. Off
    > southeastern Connecticut there are numerous lighthouses  seemingly at every
    > direction
    > around the horizon. So I measured all possible  horizontal angles between five
    > of them and then compared. I'm still looking at  the results, but for those of
    > you who want to look for arc error, this seems to  be a good way to do it. It
    > follows from the simple fact that the angles should  add up: if the angle from
    > lighthouse A to C is 120.1 degrees while the angle  from A to B is 50.0
    > degrees and the angle from B to C is 70.0 degrees, then  there must be arc
    > error up
    > around the high end of the sextant arc. This sort of  thing might serve as a
    > consistency check for tests done with star-star  distances, etc.
    
    
    

       
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