Study the sketch, then it returns with a few changes. Click each change for +1 point. Every level is harder: less memorize time, more changes. You only get 5 wrong clicks for the whole game, plus a bonus try every 3 levels.
A 4 to 8 digit number flashes up. Memorize it, then answer three tricky questions about it. A wrong answer costs a life, and you have 3.