Elo rating system
Other systems calculate a numeric rank for each player. This removes the limitation on which matches are allowed. The most widely known system of ranking players is the Elo rating system, which is used for Chess and Go. Every player in the Elo rating system receives a rating based on his or her win/loss record, which establishes his or her position (or level) on the "game ladder." Numerous efforts have been made to design better game ladders by analyzing the statistical correlation between relative ladder levels and a player's expected performance.