Almost identical to Scrabble, but with numbers forming equations rather than letters forming words. "The game is played with tiles numbered 0 to 12 and tiles showing mathematical signs and parentheses. Each tile has a score (except the equality sign and parentheses). The most valuable numeral is 7 (because it has the least options for making an equation that equals 12 or less) and the most valuable signs are division and multiplication (again because there are less equations involving these operations that equal 12 or less). Like scrabble, squares on the board can increase your score, whether an individual tile or for the entire equation." Source: http://www.dicemaestro.com/vintage-games/retroactive.asp