The "U", the "O", the "A" and the "C" on the Weston dial are essential parameters for exposure. One of ye olde lab ratz who shared their wisdom with me back in the early 1960s said that the best treatise on exposure was found in the Weston Master instruction manual, using those four letters.
Weston revised the calculator dial each time. Personally I think the Master IV dial is the easiest to read, it's got a roulette arrangement. Once you spend a few minutes figuring it out, it's easy to decypher. The Ranger 9 is nice, but it's also physically larger so everything's a little easier to read (IMO).
My favorite comes from a Sekonic L-228 zoom. Big dial, easy to read numbers. I think it was highly influenced by the best of the Weston dials.