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    Re: The Noon Fix
    From: Frank Reed
    Date: 2009 Apr 8, 12:15 -0700

    Jim, you wrote:
    " It is not a running fix, since no lines of position are advanced or retarded. Or even determined."
    
    If you're adjusting the sights for motion of the observer, that is equivalent 
    to a running fix. So unless you're explicitly reserving the expression 
    "running fix" for the case of plotted LOPs, I don't think there's any problem 
    calling it a running fix, and that may be helpful explaining the method to 
    navigators who already understand that concept.
    
    This whole business of generating a fix by a series of sights around noon is a 
    subset of a general case which I have labeled (in the absence of previous 
    terminology) a "rapid fire fix". If you take a series of multiple Sun sights, 
    oner after another, over a fairly short time interval so that the Sun's 
    azimuth changes by a moderate amount (let's say twenty degrees), then you can 
    reduce these sights, perform a least squares analysis, and get a fix that is 
    surprisingly accurate. This is a type of running fix since each sight has to 
    be advanced/retarded based on the observer's motion.
    
    In a general "rapid fire fix", the position is clearly more accurate in the 
    direction of the Sun's azimuth just as the particular case of sights around 
    noon yields a latitude that is more accurate than the corresponding 
    longitude. The accuracy in the perpendicular direction is lower but increases 
    rapidly either by multiplying the number of sights or by allowing for a 
    larger change in azimuth. 
    
    -FER
    
    
    
    
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