The game that inspired Code 777, this one involves deducing the 3 number cards that you wear in a band strapped to your head. Unlike Code 777 there are no colors involved just the numbers 1-9. On your turn you ask a question aloud and then answer it. The questions involve the numbers you can see on your opponent's heads, like sums, odds vs. evens, etc. The questions on each card are ranked in difficulty so you can vary the difficulty depending on the participants.
Using the answers to the question you race to deduce your number. If you get it wrong you keep the three numbers, but lose 4 points. If you get it right you get 10 points and 3 new numbers on your head. First person to some set total wins.