Key at top left of numeric keypad

It's Number Lock.

BTW don't expect it to light up.

I don't know why you would need a "Num Lock" key on the Pro keyboard. But on the newer keyboards it is labeled "Clear" and that is what it does in the Calculator Application.

Some applications require the number lock to be enabled before they use the numeric keypad. Without it, the numbers won't do anything. Even though the number lock doesn't actually change anything for the Mac OS, it may still need to be on because an application looks for it.

-Doug

Really? Interesting, I haven't run across any that require that yet.

That would certainly be a secret key on the new keyboards since the "Clear" key doesn't say "num lock" any more.

It's been a long time since I've come across one. I couldn't even find a recent example. Apple must think it's no longer necessary.

-Doug

The new Apple keyboards don't have a light & the key is labeled "clear." When you use an older Apple keyboard on a PC (as I do at work), it does light up for "num lock."

Hi Darren,

Thank you for the enlightenment. I have been looking for a "num Lock" key on the Mac keyboard to operate my KVM switch (using hotkey). I thought there isn't such a key and I used a PC keyboard instead. Now I can use my Mac keyboard again.

TS

My numeric keypad suddenly stopped working. All of the keys on it work except the #s , and when I press the clear button I get a doink. At one point, pressing any of the keys would disable the keyboard entirely. I thought the computer froze, but after hitting some of the numbers on the keypad, the keyboard came back and allowed me to type. Any clues as to what is going on with my keyboard?

Go to system prefs>universal access and see what inadvertently got turned on in there. Probably Mouse keys.