This application was designed to be used by anyone who wants to calculate the expected score, rating change, and performance rating of their chess games. This app uses FIDE's official rating rules.

The rating system used in this app is based on the Elo system, which was developed by the FIDE (Fédération Internationale des Échefs de Montréal) in the 1970s. The ELO system is used by many different organizations to rate the performance of chess players.

The basic idea of the ELO rating system is to give each player a score based on the outcome of their games, their performance in other games, and their achievements. This is done by calculating the player's "ELO score", which is based on the result of their last game, the performance of their opponent, and their previous performance. This calculation is done using the ELO formula, which is based on the game's duration and the number of game moves played.

By using this app, you can calculate the ELO score of your chess games and get an idea of how good or bad you are.