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    Re: typical standard deviation?
    From: Jeremy C
    Date: 2009 Aug 15, 11:55 EDT
    I can provide all sorts of data for people with more of a math bent, but i am but one observer.
    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.
    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.
    In a message dated 8/14/2009 6:17:26 A.M. Central Asia Standard Time, maartenvannoorden@gmail.com writes:

    >EXCELLENT!  I am afraid that with so few people such as myself out  here
    who actually practice celnav, our hopes for at sea data are fairly
    especially from the larger vessels.

    >I wouldn't expect to find such data. During the history of celestial
    navigation _IT_ was the most accurate navigation system available so
    there was no other data that the celnav positions could have been
    compared with to develop such an accuracy data set. Really, only since
    the development of GPS (maybe LORAN C) has such another set of
    become available so only now can such data be developed. But how many
    navigators continued to use celnav on a regular basis and then logged
    the accuracy of the celnav position derived after comparison with the
    contemporary GPS positions and then made their logs available.

    Acually you don't need an exact GPS nor a hugh amount of people to
    estimate the error. A good way of doing the analysis would be to use
    what is called a 'MSA' (Measurement System Analysis) and is used in
    industry to distinguish between operator errors and machine errors. A
    simple setup would involve one sextant, one ship and 2 or 3 operators.
    The operators (users) will shoot in random orders with the same
    instrument and calculate their position. The total variance (square of
    the standard deviation) is the sum of the variance of the inter
    operator error and the error caused by the measurement setup.

    If you want to include all types of potential errors due to for
    instance horizon (as mentioned above), you can either instruct the
    operators very well (the error will be in the test setup) or not at
    all (the error will be in the operator part).

    If the experiment is carried out at the same location, no GPS fix is
    needed or desired, it will add an extra variance to the equation (but
    probably very small)

    If somebody is willing to carry out this experiment, I am more than
    happy to assist with the statistical part.


    Maarten van Noorden
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