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    Re: AN5954 bubble octant by Bausch and Lomb
    From: Alexandre Eremenko
    Date: 2012 May 5, 10:31 -0400

    Gary,
    
    This time it is the right sextant, thanks.
    (I have not figured out yet how can one search and find anything
    in the list files database:-)
    
    Unfortunately the description is too brief, and some parts of it
    are not clear.
    For example, the sentence that "the interval between two series
    must be approximately 6 seconds".
    During these 6 seconds you are expected to:
    
    a) read and record the reading, (which involves "rotating the drum until
    the median index is under the index line"),
    b) reset the scales
    c) find the star again, and align it with the bubble
    
    All these steps they recommend to do in 6 seconds:-)
    Seems unrealistic to me.
    
    The details are still not clear, but apparently they assume that when
    you shoot VERY quickly (once every 6 seconds), the change of the altitude
    during the time of observation (90 seconds) can be neglected.
    In fact, this change can be as large as 22', but under normal conditions
    (lattitude not too small) it is less.
    
    Anyway, they are apparently assuming that the effects of acceleration
    of the airplane are larger than the effect from the change of altitude
    in 90 seconds.
    
    Moreover, they recommend to use the average time of the beginning and the
    end of two observations. For one observation, the time can be 45 sec
    off the actual moment of the selected shot.
    
    So it looks like they are aiming at roughly 10'-15' accuracy under the
    best
    conditions.
    
    Alex.
    
    
    
    
    

       
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