CASIO fx-991ES Easter Egg - Diagnostic Mode

Turn on the calculator:
* Press [ON] whilst holding [SHIFT]+[7]. Calculator can be on or off.
* Press [SHIFT] five times to cycle through the various screen modes.
* Press [AC]
* You can change the LCD contrast using D-Pad [<] or [>], when you are done, press [AC].
* Press [SHIFT], [ALPHA], [UP], [RIGHT], [MODE], [CALC], [INTEGRATE], [LEFT], [DOWN], [X-1], [LogBaseN].
* Then press the remaining buttons, one after the other, from top-left to bottom-right.
* Then, as instructed, press [ON] to return to the default mode.