RPN

Simple fixed-point decimal arithmetic, Reverse Polish Notation calculator. RPN

calculators may be in the minority but they are easy to learn and very

efficient. The idea is that the operator follows the operands, so that instead

of typing 2 + 2 =, one types 2 enter 2 enter +. The left arrow either deletes

the last digit or drops the last item from the stack. The up arrow show a few

other functions such as setting the number of decimal points, swapping items on

the stack and the use of exponents.