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    Re: Lunars and the Astra IIIb
    From: George Huxtable
    Date: 2001 Dec 16, 5:06 PM

    In this thread about lunars, John Kabel said-
    
    >Prudent navigators will know that sextant navigation has a large
    >error circle when compared with GPS.  This is likely to reopen a
    >debate about errors on this list.  I recall that we at one time had a
    >thread, in which error circles of three to ten nautical miles were
    >discussed.
    
    My response-
    
    In the case of longitude measurement by lunar distance, and latitude
    measurement by noon Sun altitude, there would not be an error circle, but
    an error ellipse, much wider in longitude than it is high in latitude.
    Likely errors of 3 to 10 minutes (miles) for latitude error seem reasonable
    (perhaps 10 minutes is unduly pessimistic except in rough weather). But an
    error of 30 to 60 minutes in longitude would be quite good going for the
    lunar distance technique.
    
    He also said-
    
    >I have an Astra that had no index error for the first year that I owned it.
    
    It puzzles me why navigators worry about index error, seeing that it's so
    easy to check and allow for. But I accept that a constant zero index error
    might give some confidence in the general stability of the instrument. The
    important factor, however, is the precision and uniformity with which the
    rack has been cut.
    
    George.
    
    
    ------------------------------
    
    george---.u-net.com
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.
    ------------------------------
    

       
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