If you can do addition and subtraction in your head, you're in the wrong business. Go do something else, perhaps something rewarding. But for the rest of us, this mathmaking genius machine can be yours for $8.00. Which is twice as much as $4, but $4 less than$12.00. See how much fun it can be! Also very useful for proving to the people in finance how you racked up over $200 in expenses.