 The Elo system was originally invented as an improved chess-rating system over the previously used Harkness system, but is also used as a rating system for multiplayer competition in a number of video games, association football, American football, basketball, Major League Baseball, table tennis, board games such as "Scrabble" and "Diplomacy", and other games.The difference in the ratings between two players serves as a predictor of the outcome of a match.Two players with equal ratings who play against each other are expected to score an equal number of wins.