dist/flow.js
function () {
      var timeSpan = Date.now() - this._lastProgressCallback;
      if (!timeSpan) {
        return ;
      }
      var smoothingFactor = this.flowObj.opts.speedSmoothingFactor;
      var uploaded = this.sizeUploaded();
      // Prevent negative upload speed after file upload resume
      this.currentSpeed = Math.max((uploaded - this._prevUploadedSize) / timeSpan * 1000, 0);
      this.averageSpeed = smoothingFactor * this.currentSpeed + (1 - smoothingFactor) * this.averageSpeed;
      this._prevUploadedSize = uploaded;
    }
function () {
      var timeSpan = Date.now() - this._lastProgressCallback;
      if (!timeSpan) {
        return ;
      }
      var smoothingFactor = this.flowObj.opts.speedSmoothingFactor;
      var uploaded = this.sizeUploaded();
      // Prevent negative upload speed after file upload resume
      this.currentSpeed = Math.max((uploaded - this._prevUploadedSize) / timeSpan * 1000, 0);
      this.averageSpeed = smoothingFactor * this.currentSpeed + (1 - smoothingFactor) * this.averageSpeed;
      this._prevUploadedSize = uploaded;
    }
Update speed parameters
@link http://stackoverflow.com/questions/2779600/how-to-estimate-download-time-remaining-accurately
@function