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    Re: Averaging
    From: George Huxtable
    Date: 2004 Oct 19, 21:51 +0100

    Chuck Taylor sent this message-
    >George Huxtable wrote, concerning the concept of
    >averaging observed sextant altitudes over time:
    >"But I don't see how you would apply that
    >technique to a quantity that was changing
    >systematically, in the way that observed altitudes
    >change rather steadily with time (either
    >increasing or decreasing), with a bit of random
    >scatter superimposed."
    No. Chuck has that quite wrong; perhaps I didn't make myself clear..
    That's what I wrote, in response to a posting by Federico Rossi, but it
    wasn't "concerning the concept of averaging sextant distances over time."
    Federico Rossi had written, about averaging an odd number of observations-
    >The explanation I've found for this recommendation is that this way you
    >can consider the central value of the odd series (i.e. the so called
    >median) which is definitely less affected by abnormal values than the
    >average value.
    And I replied-
    "Selecting a median that way seems to be an alternative to averaging. It's
    a rather extreme case of discarding outliers, in that it discards
    EVERYTHING but the one median observation.
    I can see that it might be usable (if not ideal) for dealing with a
    quantity that fluctuates in a random manner. But I don't see how you would
    apply that technique to a quantity that was changing systematically, in the
    way that observed altitudes change rather steadily with time (either
    increasing or decreasing), with a bit of random scatter superimposed."
    What I didn't see, was how you could apply the technique of CHOOSING A
    MEDIAN VALUE (as Federico suggested) to a series of measurements that
    varied with time, as altitudes do.
    I see no problem, none at all, in applying an AVERAGING technique to such a
    series of measurements.
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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