For reference here are the different calculator keys and what they do. My thinking was that working out what the different symbols did would be part of the puzzle, but that may have been overcomplicating the gameplay.
Multiply by 10
Multiply by 10 add 1
Multiply by 10 add 2
Multiply by 10 add 3
Multiply by 10 add 4
Multiply by 10 add 5
Multiply by 10 add 6
Multiply by 10 add 7
Multiply by 10 add 8
Multiply by 10 add 9
Equals sign
Push 0 onto stack
Add top two entries on stack
Difference between top two entries on stack
Multiply top two entries on stack
Square top of stack
Cube the top of stack
Reverse digits in the top of stack
Duplicate the value on top of stack
Sum the digits in the value on top of stack