Total posts : 45366
RPN calculators are great. I have used them for a long time and still have two that work. In fact, there was a method of using a slide rule, which I think was called chaining, which also speeded up calculations though it was not RPN. If I recall right this was used when you had products over products and it was faster to do each quotient rather than do the top and bottom products. Similar to RPN this put the answer you needed from the preceding operation at the scale “1” so it was ready for the next operation.
Back in the day when nurses in our ICU did drug mixing the decision was made to teach them how to use slide rules for the calculations required. We bought a crate of small plastic Picketts for a couple of bucks each and guess who was assigned to teach them how to use them (the engineer on faculty instead of the MDs). Some struggled but most adapted quite well when they saw how much easier slide rules were compared to pencil and paper.