Stay always on top: Calculator stays on top of all other windows if checked.
Copy display to clipboard on exit: Copies the display's contents to clipboard, so that you can paste them elsewhere. This occurs when you close the calculator.
Mode Style: Select between arithmetic operations (+,-,*,/) or bit manipulation operations (OR, AND, XOR, shifts,...).
Base: Select between Hexadecimal, Octal or Decimal numbers. When calculator is active, you can change the base by clicking the red caption.
When you click OK, all options are saved so that they will be default when you start again calculator. If you click cancel, no options will be saved.