Simple RPN Calculator

This is a simple RPN (Reverse Polish Notation) calculator designed for basic mathematical calculations. It is designed to replace the four function algebraic calculator found on android phones. The calculator display shows the top four values on the stack (X, Y, Z, and T for those familiar with HP calculator terminology), and holds up to 46 more. In addition to the add, subtract, divide, and multiply functions, the calculator also includes a square root and power function.