The weight index determines how many points are exchanged per game. A low weight index (10 or lower) would lead to a long-term-ranking where results from the distant past still have an effect on todays Elo values. A very high value instead would be a good indicator on current shape of clubs and recent results.
This ranking uses the weight index that allows the best prediction for the next match. Simulations for every weight index have been performed and compared. At a weight index of 20, the difference between the actual results and the result expectations are at a minimum (least-squares).