A calculator with a "flip display vertically" button can be very interesting! I mean, you can press that button to show tricks like this to your friend. But it can also be used by service staff (think insurance people, car sales people) to do the calculation on their calculator and then just press the button to flip the result and show the result to you. You don't have to turn the calculator upside down because the button can flip the output!

Or a calculator with two displays. One for you, and one for the customer. I think many cash registers already have something like this. Segment displays are cheap, so it makes sense.