code: function () {
  		var series = this.series,
  			i = series.length;
  		if (!this.isXAxis) {
  			while (i--) {
  				series[i].setStackedPoints();
  			}
  			// Loop up again to compute percent stack
  			if (this.usePercentage) {
  				for (i = 0; i < series.length; i++) {
  					series[i].setPercentStacks();
  				}
  			}
  		}
  	}
docs: Build the stacks from top down