Offline calculator that works

Good afternoon: I am contacting you to see if you could recommend a calculator app for a friend’s phone. It should not have any strange connections or unnecessary or strange permissions… He tried Fossify Calculator Beta, but he says that some keys don’t work when he presses them. And it’s not the device, because the screen works fine. And the Samsung Calculator works fine. But he wants to remove the latter, as it has many unnecessary permissions and Internet access, etc… Thank you for your help and time. Best regards