Hello all.

Perhaps you could shed some light on this mystery. A very intriguing curiosity is why the 4515 (Mathematician) incorporated a 3-level RPN without either R^ or Rv but the 4525 Scientist had a 4-level stack with a Rv manipulator which does facilitate R^ by way of a trio of Rv strokes. So, what was the point of a 3-register RPN stack without even stack manipulation keys?