code: function Glicko2(settings){
          settings = settings || {};
  
          // Internal glicko2 parameter. "Reasonable choices are between 0.3 and
          // 1.2, though the system should be tested to decide which value results
          // in greatest predictive accuracy."
          this._tau = settings.tau || 0.5;
  
          // Default rating
          this._default_rating = settings.rating || 1500;
  
          // Default rating deviation (small number = good confidence on the
          // rating accuracy)
          this._default_rd = settings.rd || 350;
  
          // Default volatility (expected fluctation on the player rating)
          this._default_vol = settings.vol || 0.06;
  
          // Default volatility calculation algorithm (step 5 of the global
          // algorithm)
          this._volatility_algorithm = volatility_algorithms[settings.volatility_algorithm || 'newprocedure'];
  
          this.players = [];
          this.players_index = 0;
      }
docs: =========================  Glicko2 class =============================================