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Hi Alex,

> I agree: it looks like an excentricity error.
> Have you tested the sextant in practice?
> It can give good results with corrections applied.

Yes, I used and tested it and with corrections applied 
there is no problem at all. Just another cumbersome 
correction in the sight reduction.

Making a bespoke refraction table that incorporates the 
correction for instrument error is a good idea. I do 
however frequently use an artificial mirror horizon. 
In this case the combination with refraction 
correction does not work.

I made a sine approximation of the error curve and 
calculated a correction table in 5� increments in 
decimal minutes, to simplify handling.

A couple of weeks ago I took a series of observations 
of Mars with the Freiberger and with my SNO-T. About 
10 shots each, changing instruments after every 
observation.
All instrument corrections applied the plotted sights 
are on a straight line, no reason to complain. Any 
deviations at random, normal observation inaccuracy.

I just wonder why Freiberger is not consistently 
producing "good" instruments, given the long 
experience and likely high quality machinery they are 
using.


Best regrards
Wolfgang

   

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