Probably a Shimano on-topic "indexing" system more important than Positron was the Dura-Ace AX RD, which also had detents built into the derailleur. I don't think Shimano called this "indexed" at the time, as they were emphasizing the aerodynamics, but it definitely shifted in "steps".
Regards,
Jerry Moos Houston, TX
Kurt Sperry <haxixe@gmail.com> wrote: ...and with the detents built into the derailleur as they should logically
be! Kurt Sperry Bellingham WA
Oh, but Chuck you're forgetting that fine range of Positron stuff from the 70s. Front freewheeling, index shifting, and the ability to shift while coasting what's not to love? best, Brandon"monkeyman"Ives