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> Federico Rossi wrote
> >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.

Which is why (in this country, at least) the average price of houses, for example, is given as the median
value. It avoids the extremes that might muddy the mean.

Getting back to nav, the process for averaging sights is simple and effective. As many sights as possible
taken over about 5 minutes of time are plotted. Time is the horizontal axis, observed altitude on the
vertical. The slope of this group of sights either rises; obs to the east, or 
descends; to the west. This slope
is then compared to a calculated line, which is then best fitted to the slope 
of sights. Any extreme outliers
are disregarded (probably best, although it goes against ideal statistical practice).

It works very well, regularly giving me a result better than any observed 
value. Another advantage is that
any point along the line of best fit can be used, either a chosen time (useful 
for calculating longitude with a
sight due east or west) or a chosen altitude - within the range, of course.

Simple and effective. I'm always vaguely surprised its a technique not more widely known.

   

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