Anselmo, I gave the start to the discussion about "typical twentieth century sundial concepts" after remarking that some concepts were missing in the survey of Margaret Stanier in the BSS Bulletin volume 14 (iii) of september 2002.
Bifilar dials are not missing in this survey. Willy Leenders Hasselt, Flanders in Belgium Anselmo Pérez Serrada wrote: > Hi all, > > I do not know if bifilar dials are or not an outstanding > contributions to sundialing in the XXth century... Among > other reasons, because I know the general idea of them (from Scientific > American) but not the details. However, > as far as I know bifilars were invented in 1922 ... I think that these > and the conical sundial are the best ones for > a single reason: they are completely classical, ie., they could as well > have been discovered in the XVth century > or in any other. > > Best regards, > > Anselmo > > - -