The optional game defined Elo score for the client making the request. The Elo score is averaged against all clients in a match and that value is used to produce better search results when listing available matches. If the Elo is provided the result set will be ordered according to the magnitude of the absoloute value of the difference of the a client searching for a match and the network average for all clients in each match. If the Elo score is not provided (and therefore 0 for all matches) the Elo score will not affect the search results. Each game can calculate this value as they wish according to whatever scale is best for that game.