> […] the calculator uses Reverse Polish Notation (RPN) to input calculations, simplifying the hardware design but making it more difficult to use.

I would argue against this statement which I’ve seen many times. RPN is not more difficult to use, it is simply different from what people have been using for the last few decades. Not being used to an human-machine interface and having to learn it should not be confused with difficulty of use.

Someone used to vi/vim has all the ease in the world to use it, but it might take a newcomer more time to adapt.

RPN has a very natural data waterfall flow, especially when stacks can grow to multiple levels. Of course you don’t have a direct view of it, but it becomes second nature. You simply know what that the higher value in the stack is your previous result.