On the Subject of Devilish Calculations

Is Dr. Kawashima trying to train your concentration or break it?

Note: If the expression on the first activation accepts its correct answer, you are looking at the wrong manual.

A “Devilish Calculations” module has a keypad with ten of the keys labeled from 0 through 9, another key labeled with a dash, and the twelfth key labeled with an equals sign.
Upon activation, the screen on the top left of the module will display an expression with single-digit numbers.

By default*, the first and second activation prevents the defuser from inputting anything. The buttons do nothing but play a sound effect.
On the third* activation, a fanfare plays. This sound signifies that the defuser may now input and submit solutions. The current input is displayed on the top-rightmost screen.
To deactivate the needy, submit the solution to the expression two activations* before the current one.
A strike will be given if the timer runs out or when you submitted an incorrect input.

There is never an expression with a negative answer. The dash key instead resets the defuser’s input.

*Through the mod settings, the defuser may alter how many expressions back they want to recall. The default settings is 2-Back, though 1-Back and 3-Back may also be an option.