Is it actually frozen, or just busy? A long calculation or a graph that is still drawing can look like a freeze: the screen sits still, often with a moving busy indicator in the top-right corner. That is not a crash. Press once (a single tap, not held) to interrupt it: the calculator stops and shows ERR: BREAK, and 1:Quit returns you to the home screen. Only if the screen ignores this is it genuinely locked.

Switch it off and on. Still stuck? Press to switch off, wait a moment, then to switch back on. A locked screen almost never means a broken calculator. It usually just ran its battery low mid-calculation, and a power-cycle clears it. If even and are dead, move to the reset button.

The reset button on the back. Turn the calculator over: near the top is a small recessed hole with a button inside. Press it with the tip of a pen or a straightened paper clip and hold for about two seconds, then release. The calculator reboots. This is the safe reset: it keeps the operating system and anything you have archived, and only clears RAM, meaning the home-screen history and any lists or values you had not archived. In an exam that is exactly the trade you want.

The combination to never touch. Do not hold and while you press reset. That does not reboot: it erases the operating system and leaves the screen showing Waiting… Please install operating system. The only way back from there is a computer running TI Connect CE, which you will not have at your desk. If your screen is already showing that message, this calculator is out for the paper. Put your hand up for a spare.

Prevent it: charge the night before. Freezes almost always trace back to the battery. The TI-84 Plus CE runs on a rechargeable battery, so charge it fully before every exam; if it has sat switched off for months, give it a few hours before you trust it. A calculator that keeps freezing on a full charge should be replaced, not relied on.