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Jim,
What you are saying is very interesting.
When you have time, would you post (or send to me)
some specific data?

> For what it's worth, I have found that under good conditions
> measurements  are typically within 0.7' most of the time (say  90% of the time) and
> within 0.3' about a third of the time.

What sextant do you use? What sort of measurement you are talking
about (Sun altitudes with real/artificial horizon? Star altitudes?
Lunar or star distances?)

> I have noticed that there can be some significant differences (0.3 at  times)
> depending on the source of the almanac data at times.

I only use two sources: THE Nautical Almanach (on paper, commercial
edition, which is guaranteed to be identical with the Govnmnt edition)
and Frank's web calculator for the Lunars. Couple of times I reduced
my lunars myself using the same Almanach, and the result
(rounded to 0.1') was exactly the same as Frank's calculator gave. So I
trust
Frank's calculator (coupled to an electronic almanach).

Another source of error I encountered was the use of various simplified
reduction
tables. (I suppose HO tables cannot introduce the error of 0.1', but
actually I never checked this. My prefered method is Casio f-calculator
which I trust completely. This calculator was recommended (as the best
calculator
for Cel Nav) in a Russian book of 1980 ! Such a pity that
production of this wonderful
thing was discontinued! My one is 17 years old, and I see nothing as good
on the market today. But I hope it will serve another 17 years unless
I drop it to the sea:-)

Alex.

   

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