Hello Peter, Wow, The Dodwell dial is amazing! I wish I had some better pictures so that I could see it in some more detail. The surfaces appear to be of the "Astroid/Evolute of an Ellipse" type. I assume the "unwinding of the analemma" is by multiple gnomons? This has given me an idea for a different kind of polar dial that covers all the hours. I've got to think about this one. I too am at a loss as to how he made it in the 1940's! There were some cam fed machining tools that could have done the basic curves of the design, but laying out the actual hour lines must have taken a long time.
Thanks much!, Edley McKnight [43.126N 123.327W]
