Quote: Av = Aperture value (aka Aperture priority) expose shot.
Tv = Time value (aka shutter priority)
This is something which lead to some confusion for occasional shooters back in the eighties.
Until then it was called
Time Automatic . . . . . . =Ta (today Av)
Aperture Automatic . . .=Aa (today Tv)
So the expressions were just reversed.
To make sure, I just looked it up in old (German) Pentax manuals.
There they don't mention Aperture or Shutter priority, but name it Shutter or Aperture AUTOMATIC.
This is in line with the handling of cameras before they offered a mode wheel covering ALL modes.
With the Super A/Super Program, you set the aperture to "A" to get (today's) Tv, and the mode wheel to "A" to get today's Av.
I think Pentax changed this only with the S or later series; and Canon, Nikon, Minolta, and Olympus did it the same way.
EDIT: I just remember the MZ3 / MZ5 is controlled the same way as the Super A/Super Program, so the change in naming the modes may have come even later.