Harold Hallikainen via GreenKeys wrote: > This came across in another list. I had never seen it before. > > https://youtu.be/ywy6xXjwgmI There is a Bell Systems Technical Journal article on this mechanism, as well: https://ia800309.us.archive.org/16/items/bstj27-1-44/bstj27-1-44_text.pdf Ethan