Changing a number box value with the "key" object

Greetings,

This may be a simple solution, but I can't figure out anyway to get it to work. What I would like to do is make a the a number in a "number box" increase by one each time I hit the up arrow key on my computer. I've used the key command and have attempted using the + object but it still won't work. Does anyone know how to do this?