How to use it
Unlike with a traditional calculator, you enter the parameters first, than the operator.
For example, to calculate '20+50': type '20' -> Press Enter -> '50' -> Press '+'
The 'C' key deletes the input line.
The 'AC' key deletes the whole stack.
Use the 'POP' key to remove the last value entered and shift the stack down, and the 'SWAP' key to swap the last two elements.