Some advanced codes can unlock even more features:

The calculator was open to the scientific layout: sin, cos, log, asterisks and parentheses. Mina tapped absentmindedly, watching the numbers march across the display, nothing more. But a pattern nagged at the corner of her mind—an old habit of noticing when something that should be one thing behaved like another. She pressed long on the app’s icon; nothing. She swiped, checked the app info, glanced into its storage. Then she did what locksmiths always do: she tested.

You might be wondering: Why use the calculator when I can just dial codes?