It’s a "Reverse Polish Notation Calculator,” (with "Enter", "Decimal", 0-9, “ + ”, “ - “, “ * ”, “ / ” keys) displayed as a photorealistic graphic calculator with three outputs. Note: An RPN calculator does NOT require parentheses to determine the order of operation in evaluating a mathematical expression, known as postfix notation.

1) The standard output of a calculator. Located at the top of the calculator, the results of an entered and executed postfix expression,

2) An emulation of the paper tape generated in mechanical calculators. Located at the bottom of the calculator, this output displays the operands and operators in the order they were enter.

3) The “STACK.” Located below the 2nd, displayed the operands (the numbers) in the order they were entered. When an operation (+, -, /, and *) is entered the two top numbers on the stack are POPed off the top of the stack to be processed according to the operation entered. The result of the operation is then: displayed at the top of the calculator, and also “PUSHed” onto the top of the stack.

The purpose of the app is to demonstrate to students, and others, the efficiency of RPN – it saves time and keystrokes –the user sees the results of the computations are they are preformed, and in the order they are preformed – it’s logical because first, the user provides the numbers to be used in the calculation, and then the operation to be preformed, i.e., Six, Enter, Nine, Enter, Multiple, and NOT Six, Enter, Multiple, Enter, Nine, Enter.