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    Re: Sextant precision
    From: Alexandre Eremenko
    Date: 2004 Oct 4, 00:05 -0500

    Dear Henry,
    I recently mentioned my attempts to measure the index error
    the way you describe,
    by comparing Sun's lower limb with its upper limb:
    (See my message on "star-to-star distances of
    Wed Sep 29 2004 - 16:02:05 EDT, paragraph 6).
    This was one of the three methods recommended by the manual
    to my SNO-T sextant.
    
    The other two were a) measuring the distance from a star
    to itself and b) the horizon method.
    
    After many repeated measurements I found the star-to-itself
    method more precise than the Sun method. This is the case
    with my sextant, my scopes and my specific observation
    conditions, I do not generalize this to all situations.
    (Unfortunately I have no possibility to use real
    horizon at this time).
    
    I can post the numerical data if this is interesting.
    
    However I don't know of any other method (other than star-to-star
    distances) of measuring what you call "centering error"
    without special equipment.
    This should answer your sentences:
    
    > Unless I have misunderstood the intent,
    > the purpose thereof,
    > however, from a purely navigational point of view,
    > appears somewhat
    > elusive.
    
    and
    
    >Interstellar distances, to the best of my somewhat
    >antiquated knowledge,
    >were considered a second line method of determining centering error,
    
    You say that the better method was:
    
    > At one time, an instrument
    > could be sent off for testing by a system of
    > collimators,
    
    But I don't have a collimator. And many other people don't.
    Bougainville :-) who used the stars for a similar test,
    as described in the recent messages:
    Fri Oct 01 2004 - 00:42:16 EDT and
    Fri Oct 01 2004 - 10:58:55 EDT
    
    Alex.
    
    
    

       
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