New! The new version of the scientific calculator (not RPN) supports functions and editable history. Try it here.
Reverse Polish Notation (RPN) provides the quickest way to enter data in a calculator because it eliminates the need for parenthesis. It was made mainstream by HP when they implemented it in their famous programmable calculators. It is also very simple to code into a computer program. This is a simple online RPN calculator for you to try out. It's written in Javascript
How to use it
Unlike with a traditional calculator, you enter the parameters first, than the operator.
For example, to calculate '20+50': type '20' -> Press Enter -> '50' -> Press '+'
The 'C' key deletes the input line.
The 'AC' key deletes the whole stack.
Use the 'POP' key to remove the last value entered and shift the stack down, and the 'SWAP' key to swap the last two elements.