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Alexandre E Eremenko wrote:
> And on testing in Kew observatory:
> I have a paper describing the testing arrangement;
> apparently this equipment was installed in 1867.
> And indeed, I've never seen certificates older
> than that. 
>   
Although not from the Kew observatory, older certificates do exist, like 
the one on an octant box made by Pieter Holm in Amsterdam. The date 5864 
is according to Pieter Holm's own calender and refers to 1763 in the 
more generally known calendar as we use today. The certificate shows the 
following table:

Grad ....Min 
   6 ....  0
  12 ....  4
  18 ....  6
  24 ....  8
  30 .... 10
  36 .... 12
  42 .... ?4
  48 .... ??
  54 .... ??
  60 .... 2?
  66 .... 2?
  72 .... 22
  78 .... 23
  84 .... 24
  90 .... 25

The certificate can be found in the book 'Schip Recht Door Zee' by 
Willem Mörzer Bruyns (2003) at page 85. The first column shows the 
tested angle in degrees ('graden' in Dutch), the second the error in 
minutes, just as later certificates. The book can be downloaded from: 
http://www.knaw.nl/publicaties/pdf/20031017.pdf (although that website 
was down when I tried it just now, so maybe try tomorrow).

Nicolàs




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