flip mouse

One of the biggest irritations that I face when using my laptop comes when I need to use excel or some other number-intensive application. Notebooks are great because they are compact and portable, but the keyboard has no proper number pad! I was thinking, just about everyone buys an external mouse to replace that horrific touchpad; there are also devices which plug in to give the user a regular number pad. Why not combine them? Basically, you could have your average-looking mouse, but when you need to punch some numbers, flip it open like a flip-phone to reveal a number pad. Obviously the mouse would either need to be slightly large, or the numbers slightly small - but it would still be better than nothing. The x-y positioning would still be functional when "flipped open" so constant opening and closing wouldn't be necessary. However, when closed, it would be impossible to accidentally hit the numbers. Thoughts, comments, suggestions?