The puzzle is simple and nice. A little more explanation would be useful. From time to time I would select a number and then it would be locked in the off state. I wouldn't know how I did it and I couldn't get it back. This was annoying and eventually frustrating. I would have to reset an entire board to have it stop. Add a little bit more info. It doesn't even have to be a tutorial. Just in a menu off to the side. Since this action doesn't seem to be an intuitive control I assume it is a bug.