Hi Gabel,
Many thanks for those links. I have only had a chance to chase one of them up so far.
I read the Chain-bearer passage with great interest, he really paints a picture of the thrills and dangers of raising a frame.

I guess I am not suprised that the first frame is claimed by a number of places. The history of new ideas and inventions is that they often crop up almost simultaneously in two or more locations, and this may fit the facts in the case of square rule.
Thanks again