NavList:

Bill- I have an interest in the thermal stability question for frame arrangement.

I note this paper though behind the pay wall provides notes on tested results for sextant material design:
https://www.ion.org/publications/abstract.cfm?articleID=100097

I have a particular interest in how the ladder frame re- C Plath compares to the circular C&P as both are arived at early and long held designs. I would like to see empirical data of arc displacement for each design over a range of temperatures. I also have a specific interest in the C Plath "Traditional" as it was a late adoption which copies but seems to fall short in particulars of a center circle design as manufacuted by C&P. We now have regenerative design capabilities in even modest CAD software- I wonder at the frame arrangemnt which this process would arrive at given constraints such as frame material and arc displacement. Perhaps in my ignorance I am missing the key attribute of thermal change which might be variable index error not arc displacement?