A keyboard-based calculator that calculates in reverse polish notation (RPN) and the standard way (STACK). It also supports different notations for real and complex numbers.

RPN is useful for fast calculation of small numbers and small RPN expressions.

The main reason why this calculator is so fast is that it doesn't require the user to type in all the parenthesis and use the mouse to click on the buttons.

With the RPN mode, the user can simply enter the expression to calculate.

For the STACK mode, the user has to enter the expression in the usual way (i.e. (1+2) * (3+4)) but the calculation is done in the reverse order (4+3+2+1).

This means that the user has to enter the expression from left to right and the result will be calculated from right to left.