code: function(evt) {
          if (!OpenLayers.Event.isLeftClick(evt) && evt.type !== "touchend") {
              return;
          }
          if (this.mouseDragStart) {
              this.div.style.cursor="";
              this.map.events.un({
                  "touchmove": this.passEventToSlider,
                  "mouseup": this.passEventToSlider,
                  "mousemove": this.passEventToSlider,
                  scope: this
              });
              var zoomLevel = this.map.zoom;
              if (!this.forceFixedZoomLevel && this.map.fractionalZoom) {
                  zoomLevel += this.deltaY/this.zoomStopHeight;
                  zoomLevel = Math.min(Math.max(zoomLevel, 0), 
                                       this.map.getNumZoomLevels() - 1);
              } else {
                  zoomLevel += this.deltaY/this.zoomStopHeight;
                  zoomLevel = Math.max(Math.round(zoomLevel), 0);      
              }
              this.map.zoomTo(zoomLevel);
              this.mouseDragStart = null;
              this.zoomStart = null;
              this.deltaY = 0;
              OpenLayers.Event.stop(evt);
          }
      }
docs: /*
  Method: zoomBarUp
  Perform cleanup when a mouseup event is received -- discover new zoom
  level and switch to it.
  
  Parameters:
  evt - {<OpenLayers.Event>}