for years I hit C and retyped the whole number every time I made a typo in teh iPhone Calculator 😤 turns out theres a hidden backspace.
swipe left or right across the number display at teh top. each swipe deletes teh last digit you typed... thats it.. lol no more starting over because you typed 1250 instead of 125.
another small one: long-press teh result to copy it, sooo u can paste it into a message, newer iOS versions also added a viisble delete button, but teh swipe is still my favorite.