[quote][b]Posted by:[/b] Zlotty this is a very good and detailed description of the "skill" system and i think i know a bit more about it now, although it was a bit confusing. if i got it right the sigma - value goes up by winning streaks while Mu steadily goes up for each win. the sigma value controls how much your skill will decrease or increase for each win or loss but what does the Mu do? i didnt rly catch that...[/quote] Well, supposedly winning streaks are not taken in to account when the system calculates your new sigma value. The skill displayed is your "conservative" skill. MU is your real skill. Sigma is the amount of uncertainty about your skill. The other variable, K, is the factor of conservativeness set by Bungie. So the formula from the first post is your displayed skill = MU - (K * Sigma) Sigma is always decreasing. When you start it is high and as you play it is lowered. The idea is, the more you play, the more the system dials in your true skill. Initially, the system matches you against players who it is sure about to gage your performance. If you win, it keeps your uncertainty (sigma) higher. The system decides who is most likely to win prior to every match and if you perform predictable (winning when you should and losing when you should) your sigma is decreased. If you play outside of how the system has predicted (winning against higher level players) it keeps your sigma higher. There really is no way to get your sigma back up to a high level. Once you've played enough and it's low, it takes a large amount of wins OR losses to move skill levels.