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George,
In Henning Humland's "A short guide to celestial navigation" I've just
found a possible key: the median principle is to be applied not to the
altitudes, but to the intercepts calculated from these (maybe, the
advancing of the ship in the meanwhile should be taken into
consideration).
Frankly, I don't know how practical this method could be when manually
reducing sights since it implies a lot more work, but with computers it
could be fine.
Federico

-----Messaggio originale-----
Da: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]
Per conto di George Huxtable
Inviato: marted? 19 ottobre 2004 0.44
A: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Oggetto: Re: R: Averaging


Federico Rossi wrote, 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.

=================

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.

George.

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