I am using a #hp12c all the time and I love the #rpn mode a lot. If you're like me and want to use #reversepolishnotation on your computer as well, I'd like to suggest my small rpn calculator 'rpn'. It is a #cli tool, has completion, history, lots of functions, modes, stack management and you can even add your own functions using #lua. It runs on #linux, macosx and even windows.