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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.

George

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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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