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Jean-Philippe,

>   Did you try to identify an Index error or any systematic error?

I do not see how to measure the Index error directly.
Of course, if I have a large statistics of measurements from a
known position, I can see whether there is some systemaric bias
and subtract it as an index correction. But so far I do not
see any systematic bias. I mean that positive and negative errors
seem to be equaly likely.

> Did you solve
> issue of the bubble
> getting bigger during the observation

I don't know a radical solution of this, but I reduced
the problem.

1. BEFORE making the bubble I keep the sextant for 10 minutes
at the observation place to let the temperature of the
sextant stabilize.

2. AFTER making the bubble, and immediately before the
observation I release the
membrane pressure. One has to be careful after that and not
let the bubble approach its place of origin (at 10 o'clock
in the field of view) because it may disappear.

With these precautions, the bubble stays at approximately
stable size for 3-5 minutes, more than enough for several shots
or for an averager observation. Anyway, even without precautions
there are no problems with individual shots because I can
always adjust the bubble size before a shot,
and a very minor problem when using the averager.

This bubble growth phenomenon seems to depend on the weather
conditions but I did not investigate it carefully to make
definite conclusions. Sometimes it does not grow, sometimes it does.

Alex.



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