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    Re: Lat/Lon by "Noon Sun" & The Noon Fix PROVE IT
    From: James N Wilson
    Date: 2009 Apr 25, 21:11 -0700

    George:
    
    Your simulated data has thrown me for a loop. I expected to learn, but
    not to find that what I proposed is not what I expected. I started with
    your first example, not expecting to do any more. First, I had to convert
    your decimal data, which is what the computer needs, to that which is
    what is commonly used with the sextant and the almanac.Degrees, minutes
    and tenths. A bit of work, but no big deal. All of my programs input and
    output data in that format. The conversion to decimal and back is done
    out of sight. My first computer lessons stressed that, "The computer
    should work for you and never vice versa." Alas, grossly violated these
    days.
    
    The results of that first try were not good. The altitude-time slopes
    looked fine, and the ascending slope was flatter than the descending one,
    which is what would be expected from the northward motion. But the time
    from highest altitude to LAN was only three minutes, and I knew it should
    be about five. So, I reluctantly tried the second set. Worse! I was
    surprised to find that the slopes for that example were significantly
    flatter than for the first. Giant difference! Astonishingly, the ratio
    looked okay--the ascending slope was flatter than the descending one. So,
    I had to sit back and think. My method is dependent on determining the
    slope of the altitude-time lines, and therefore it is vulnerable to
    factors that distort those. But I never expected to see such a huge
    variation.
    
    As I wondered what I would do if this were a real situation, I realized
    that I would have to start taking sights earlier. The standard quoted is
    twenty to thirty minutes before maximum altitude. Your example started
    twenty-five minutes before. But with such a low altitude, I should start
    earlier. Hindsight, but that's what I would do faced with the situation.
    That intensifies errors due to changes in course and speed, but it's the
    only way out.
    
    I make my students plot their sigths, and they reluctantly do so at
    first. But they have increased confidence in them when they see that they
    fall on a straight line. The idea there is to help them select the best
    sight for reduction. Now, I once was invited to introduce a boatload of
    scouts to celestial navigation on one of the LA Maritime Institute's
    brigantines. I instructed them as to how to hold and use my sextant, and
    how to take readings. Then I turned them loose. I gave each one a single
    opportunity, and recorded the time and altitude. I couldn't reduce the
    sights, but I did plot them as they took them. I was pleased that they
    all fell on a straight line. That meant that they were doing it right.
    Their first sights ever, and they were all good. Except for my
    granddaugher's. Anyway, I'm a believer in plotting runs of sights. Too
    see such an extreme variation in your simulated data shakes my
    confidence.
    
    So, I need a run of sights starting earlier. Maybe forty minutes before
    maximum altitude. Sorry to make more work for you, but if we're trying to
    simulate real life, it's necessary. The idea of the double altitudes
    method is to take sights far enough away from LAN to get a reasonable
    attempt at determing it. At higher latitudes, starting earlier is the
    only way to do that.
    
    Hoping for better results next time.
    
    Jim Wilson
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