r.Calc app for iPhone and iPad

This classic RPN (Reverse Polish Notation) calculator is a simple calculator for daily uses.
The calculator features a four visible level stack, the total stack size has a total of hundred positions.
A progress bar on the top of the screen shows you how the stack is full.
For now the implemented operations are;
Plus, Minus, Multiply, Divide, Opposite, Inverse.

Other facilities like swap the first two number in the stack and recall from the last operation the two arguments should simplify the life.
All keyboard errors are notified by a vibration.