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4.1 The calculation

The calculation of new Felo ratings is a three-steps process:

  1. The result value for the fencer is calculated. This is the faction of single hits that he won. For example, if the fencer won 15:10, his result value is 15/(15+10)=0.6.
  2. The difference of the Felo ratings of both fencers yields the expected result value. The formula for this can be found e.g. in the Wikipedia article about the Elo rating system.
  3. Let us call the difference between the result value and the expected result value the surprise. The surprise is multiplied by the total number of points in the bout, and the so-called k factor, See List of all parameters. The result is added to the old Felo rating. This yields the new one.

This k factor is some sort of damping parameter. If it is too high, the Felo ratings will oscillate too heavily. If it is too low, the Felo ratings will converge too slowly.