Casio Wrist Watches Easter Egg - Screen Test Mode

I've seen this easter egg in some Casio digital wrist watches, including mine.
For activating it, you must hold two or three buttons at a time. On my W-96H, they're Mode, Adjust and 12/24H (they're usually the two at the left side and one on the right side). This enters at a sort of "secret mode", showing at a first all digits on the screen, when you press Mode you see some of them only, and with Mode again you see a code (in this watch is 2500 0 40) or the screen blank. You can exit pressing any key (except Mode).

The secret mode activation changes slightly depending on the model, try different combinations..