I don't know where the notion that RPN is more intuitive comes from. My dad had an HP-45 when I was a kid and I didn't quite grasp the concept of a stack. You've also got it wrong in your example (you've got stack 1 and 2 reversed in step 2), so I guess it's not that obvious for grown ups either! When you write a formula on the blackboard it is something like (5+6)*3, not 3⏎5⏎6⏎+* or whatever. Takes a bit of mental gymnastics to convert between the two, and you need to keep the state of the stack in your head as you go. Not really viable for anything too complicated. I guess that regular calculators suck for that too, in my opinion the best are symbolic calcs where you enter the formula as you would write it, parenthesis and all, which as a bonus allows you to go back and fix mistakes and reuse formulas easily.