Comment by dfdz

HP Prime on Reverse Polish Notation (RPN) mode [1, Page 47]. RPN is a basic stack based programming language, which is really fun to use [2].

[1]https://h30434.www3.hp.com/psg/attachments/psg/palm-webossof...

[2]https://en.m.wikipedia.org/wiki/Reverse_Polish_notation