NavList:

The diagram opposite page 187 of ‘Precision Astrolabe’ isn’t very clear.  The diagram on page 163 of ‘Taking the Stars’ is better, but it still doesn’t tell you everything.  I went to the British Library and photographed the pages of ‘Precision Astrolabe’ covering Figs 22 and 23.  These pages don’t seem to be available on-line. Unfortunately, I didn’t record the page number, but my photograph can be found here:
http://fer3.com/arc/m2.aspx/What-this-this-sextant-DavidPike-mar-2016-g34846 .  Looking at it again, I can see that if I’d looked at it properly the first time, I wouldn’t have had to ask Bill the questions I did.  Presumably, you had to tilt the frame a fraction the get the body to appear on the natural horizon, in the centre, or in the bubble.  DaveP

Look at page 187 of "Precision Astrolabe" that I previously posted.

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On Sat, 4/30/16, David Pike wrote: Subject: [NavList] Re: The Observer’s Book on Astro-Navigation - Coutinho sextant To: garylapook---.net Date: Saturday, April 30, 2016, 4:43 PM BillIt would be very useful if in addition to your other excellent photos you could get a photograph of the view of the bubbles down the eyepiece to supplement the diagrams on page 163 of 'Taking the Stars'.  Also 1, does the Coutinho require fiduciary marks for the longitudinal bubble, or is the radius of the level cunningly matched to something?  Also 2, how does the Coutinho allow for the fact that the body is focused at infinity, and the levels are about nine inches in front of the observer’s face?  DaveP