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Jared,

> also on Ebay tonight is Trommelsextant 762148 showing certified
> "corrections" that, throughout, never exceed one-half moa

From my observations of certificates on e-bay, I can conclude
that typical maximum correction for Freibergers is about 20".
But sometimes it is larger.

> The certificate is dated 1984 by a testing firm located in West Germany
> (with locations in Hamburg and Bremerhaven), and whose work, the
> certificate says, was officially recognized by the (West) German
> Hydrographic Institute.

This means that the certificate is given by another firm,
not the manufacturer.

The manufacturer is is the town of Freiberg, East Germany.
(Yes, Communist:-)

And I agree with Frank, that a sextant with large arc error,
can be good if the error is carefully determined and used to correct
the reading. And that issuing honest certificates is much better
than just writing "Good for practical purposes", and keeping it
secret what does this exactly mean.

> Is the worm defective? Are the teeth on the limb spaced improperly?

I duppose that this pattern (smoothly
increasing error towards the larger
angles reflects the fact that the center of rotation of the arm
does not coincide with the geometric center of the arc.
That's why they call it excentricity, btw. It is common on many
sextants to have larger errors towards the arc end.

So the geometry seems clear. For the possible technical reasons of this
excentricity, Bill M probably can tell more, this has to do with
journal, bearing etc.

Alex.

   

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