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    Re: Please tell me if I have this right
    From: Peter Fogg
    Date: 2006 Apr 19, 08:02 +1000

    Robert Gainer wrote:
    > I would think that if you don't know the amount of error (drift from
    > unknown current) you couldn't build in a correction.  The unknown is just
    > that, unknown.
    
    The major ocean currents are well known, although of varying speed. Tidal
    movements around coasts and counter currents (running in the opposite
    direction to the main one close to the coast) can be bafflingly
    unpredictable.
    
    Greg wrote:
    > ... some error would have undoubtably crept in due to
    > unknown currents etc.
    
    One of the 'etceteras' could be leeway; another drift due to windage (the
    same thing on a power vessel). These can and should be evaluated and
    corrected for, as normal navigational procedure.
    
    > and it would not be impossible for the actual
    > lattitude to be off by 2-4 miles.
    
    I don't think anyone would worry about such a tiny discrepancy in 1780.
    Remember that Cook thought the problem of longitude had been solved by
    lunars. He seemed to think that being 30 odd miles off was pretty good, and
    so it was, then.
    
    
    

       
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