NavList:

Grateful thanks to Frank and Roger Connor.

Yes indeed, this is exactly what I have been looking for.

I decided to build a replica based on the photograph of the AX side already on the Smithsonian website.Harri Ojanen,(who produced the computer generated curves ) and I took a guess as to the likely layout of the BY side ( the dark side as I called it!), based on the descriptions in the 2 key papers by Brown and Nassau and the more recent one by Luykx.

I attach my build description notes. As you can see, we got it very nearly right, although the Vernias look a little different. Perhaps Harri, if you are  still active with  this, you could check your  Vernias against these 2 pictures?

Despite the Vernia issue, I seem to get accurate results with my replica. (well, +/- about 5'.  often better  if I use whole number intergers for LAT and LHA)

Many thanks again.Good team effort!

Best wishes

Francis

P.S by the way, I managed to persuade a nice lady at the NMN, Greenwhich to supply photographs of the Bates astronomical slide rule,(expecting them later this week), so watch this space. I feel another replica build project coming on!