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    Re: typical standard deviation?
    From: Frank Reed
    Date: 2009 Aug 15, 10:21 -0700

    Jeremy, you wrote:
    "This might be something to try at the bi-annual gathering at Mystic with 
    lunar distance measurements.  A number of observers with the same sextant 
    taking say 10 observations or so each should be able to come up with some 
    decent data to begin with."
    Speaking of Mystic, I'm looking at late Spring 2010, roughly eight months from 
    now. Anyone have any dates they would like to exclude? 
    I've organized three meetings in Mystic where we had planned to have a group 
    of people shoot lunars and compare results. Two of the events had murky 
    weather: high cirrus and some haze so the results were not all that good. But 
    at the first event, back in September 2005, we had eight people shooting 
    lunars and six got excellent results, all within 0.2 minutes of arc of exact. 
    One was off by about 0.5 minutes of arc --not bad, but not as good as the 
    majority. The last had results which differed by over 2 minutes of arc. 
    Several of us tried his sextant and had similarly wild results, so we know 
    that the blame falls squarely on the sextant in that case. And it was a good, 
    name-brand metal sextant. It had no obvious flaws and no evidence of mis-use, 
    which I think goes to show that we really need to test each instrument. You 
    can't judge a sextant by the polish of its frame or the name of the maker.
    And you wrote:
    "Sadly at sea, the only place you will get a fairly large number of observers 
    with sextants is a school ship with the cadet cadre doing their sea projects. 
     The big problem with this is that they really don't care enough for the most 
    part to try and get accurate sights and are also neophytes so will be all 
    over the place with their observations.  Still, if I ever go out on a 
    training ships as an instructor, i might look at gathering data of that 
    nature for whatever it's worth."
    Right. The fundamental problem here is that the students are not being graded 
    or judged on the accuracy of their sights. They are well aware that it just 
    doesn't matter. In many of the cases that I know of where significant numbers 
    of students are taking celestial sights today, there's no pressure placed on 
    them to do it well and do it accurately. Clearly, it's hard enough to get 
    them to do it at all, so instructors tend not to scold them too much for low 
    accuracy. One way of getting around this problem is to offer a prize for 
    accuracy. You tell the group of students in advance (so that they have time 
    to practice and hone their techniques) that the best sight accuracy will be 
    rewarded with a $100 gift certificate (not to be spent on a GPS receiver!), 
    and then they will all compete. 
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