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Alex et al,
Here's my two cents worth:

1.  In the mid eighties I was told by a British sextant importer (who
was very knowledgeable), that the German Hydrographic Office allowed
sextant manufacturers who produced sextants with no more than 20" of
error along the arc, to say Gut, or No error for practical use on the
certificate. But if the sextant had greater errors, then they had to
include a calibration certificate showing the errors every 10 deg.

2.  At the same time I saw Freibergers (called Zeiss) by the Brits
being sold as either "A" or "B" models.  The A models sold for a
slightly higher price because they had the "Gut" certificate. The B
models had the certificates showing the errors every 10 deg.  I
thought this was an honest way of portraying the fact that
manufacturing is not perfect. In the case of brass or bronze arcs,
the sextant can be brought into a high degree of accuracy by shaving
the grooves of the arc while the sextant is on the testing machine.
Whereas an aluminum arc is immediately sealed against oxidation after
the cutting process, and any further modification is impossible.
Obviously some sextants came out better than others, and I thought
labeling them "A" or "B'"was an honest way of identifying them.

Ken Gebhart
On Apr 15, 2012, at 6:21 PM, Alexandre E Eremenko wrote:

>
> Wolfgang,
>
> well, if Freibeger sold the sextant with such certificate,
> then probably this is admissible by their standards.
> Independently of this, looking at various sextant certificates
> on e-bay for many years, I noticed that Freiberger sextants
> frequently show relatively large corrections.
>
> I agree: it looks like an excentricity error.
> Have you tested the sextant in practice?
> It can give good results with corrections applied.
>
> The best test I know (short of a sophisticated equipment) is
> taking Sun-Lunar distances, and then comparng them with Frank's
> calculator.
> About a week of daily observatins in good weather permit you
> to check most of the arc.
>
> Alex.
>
> On Sun, 15 Apr 2012, Wolfgang Hasper wrote:
>
>>
>> Jean-Philippe and Alex,
>> Here's the table from the sextant case (translated :o))
>>
>> Angle ?	Correction ''
>> 0		0
>> 10		+3
>> 20		+13
>> 30		+18
>> 40		+25
>> 50		+28
>> 60		+36
>> 70		+38
>> 80		+46
>> 90		+52
>> 100		+50
>> 110		+51
>> 120		+48
>>
>> It belongs to  Freiberger Trommelsextant No. 080103 (w.
>> full sight mirror), bought early 2009, so likely
>> manufactured 2008.
>>
>> plotted corrections are fairly well resembling a sine
>> curve, which is why I assume eccentricity as the main
>> source of error.
>>
>> Any other ideas?
>>
>> Wolfgang
>>
>>
>>
>>
>>
>> : http://fer3.com/arc/m2.aspx?i=119080
>>
>>
>>
>
>

   

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