Chess rating system
The principle which lies behind a rating is this. The rating is a prediction of how well a player will perform against other players of different ratings. If the player does better than predicted, their rating goes up; if they do worse, their rating goes down. An arithmetic calculation shows by how much the player's rating changes. Today, all results are fed into a computer database, and computer software does all the calculations. Then the list is published as a 'rating list'.