code: function StdevFunction(win) {
    var self = this, m, m2, d, n;
    self.name = "stdevs";
    self.type = "simple";
    self.init = function() { m = 0, m2 = 0, d = 0, n = 0; };
    self.accumulate = function(v) {
      n+=1; 
      d = v - m;
      m = m + d/n;
      m2 = m2 + d*(v-m);
    };
    self.compensate = function(v) {
      n-=1;
      d = m - v;
      m = d/n + m;
      m2 = d*(v-m) + m2;
    };
    self.emit = function()  { return Math.sqrt(m2/(n-1)); };
    self.make = function(win) { return new StdevFunction(win); };
  }
docs: Get the standard deviation of all the things