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Alex wrote:

> Here I post some observations with my MkIXa bubble sextant.
> I will appreciate very much if someone who also practices
> bubble horizon observations will compare these data with his/her own.

Thanks for posting the results.  Interesting.
>
> Sun alt., Without averager. Average error: -0.4, sigma=2.8.

> (Bill: this is a  good example of how averaging works:
> the individual results are so-so (as shown by the sigma)
> but the average is excellent).

Understood.  I have averaged times and altitudes on the water.  It works
well. As you may recall, my preference is to plot the observations against
time and use the actual Hc line from the beginning and end to establish a
slope to fit the points to and identify outliers.  Far better than linear
regression IMHO.

On the other hand, when I had horrible horizons on Lake Michigan but guessed
at the hidden horizon line, then averaged and posted the results (very close
to Hc) you quipped it was luck, one could not trust results with a sigma
that large. 
>
> Venus alt, with averager. Error 2.6.
> Without, errors: Average error -1.7, sigma=2.
>
> Moon with averager. Error 3.7.
> Without averager, error -1.6.a

I don't see figures to support -1.6a.  What is -1.6a? What was the sigma?
>
> Venus alt, without averager,
> average 0.22, sigma 1.2

>
> Sun alt. with averager, error 0.3,
> Without averager: errors -3.5, -2.7, -3.4, -4.1, 0.0, -2.8.

Which would be average -2.75, sigma 1.4. Yes?

Looks like you are getting the hang of it. A small amount of data, but it
looks like you have a tendency to undershoot.  Can one adjust the bubble
unit to zero out any IE, or does one have to determine a bubble/IE error?

Have you attempted do place Venus or a star on the top edge then bottom edge
of the bubble and manually average?

Bill


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