The Calculator app provides large, easy-to-use buttons for basic arithmetic.
But if you turn the phone sideways, this turns it into a scientific calculator, with which you can now perform more complex calculations.
Ensure you have portrait lock disabled in Control Center – otherwise, nothing will happen when you rotate the device.
In both orientations you can tap the display to copy and paste numbers, and if you swipe across it, you’ll delete the last number entered.