NavList:

   

Reply

> -----Original Message-----
> From:  Herbert Prinz
> the discussion has gone into the very wrong direction that I was
> afraid it would. We are proposing methods to average before
> having justified
> that averaging is appropriate at all. It seems that I have not
> made sufficiently
> clear why I said from the outset that it is wrong to average the
> observations
> before reducing them. Let me therefore address this point once more.

Herbert is clearly correct to react this way to my post about Excel: on the
face of it I appeared to be advocating "willy-nilly statistics" by
suggesting that the navigator plot the run of sights on a graph in Excel,
then click around the various statistical model options until Excel produces
a line that looks cool, and then use that to produce best fit line, without
having to think hard or apply first principles.  I hasten to mention that I
was not advocating such a dangerous approach.  As Herbet points out, unless
one knows with certainty the model that applies to the body's motion for the
specific situation, and unless the correct first steps have been taken to
select appropriate sights to plot, and unless the navigator has taken enough
sights for the computer to produce a valid line, then the Excel method is
too crude.  It can, however, be a useful way to quickly double-check
situations, if the navigator bears all these concerns in mind:
http://jimthompson.net/boating/CelestialNav/MyNoonSun.htm and scroll down to
"Method 4b".   Ignore the ridiculous degree of precision in the polynomial
equation constants generated by Excel.

Jim

   

Reply