code: function() {
          var newTop = 
              ((this.map.getNumZoomLevels()-1) - this.map.getZoom()) * 
              this.zoomStopHeight + this.startTop + 1;
          this.slider.style.top = newTop + "px";
      }
docs: /*
  Method: moveZoomBar
  Change the location of the slider to match the current zoom level.