This is one of those excellent tips I can never remember. Then, when the keyboard conks out, I’m screwed. MacMost:
Mouse Keys are an accessibility feature of your Mac that allows you to control the position of the cursor and click the mouse button using only your keyboard. It can work with the numeric keypad, or with some of the keys on a keyboard without a keypad. This can come in handy if you have trouble with your mouse or trackpad and need a way to access things on your Mac.
The video is worth a view.