code: function(moZoom) {
          var zoom = null;
          if (moZoom != null) {
              zoom = moZoom - this.minZoomLevel;
              if (this.map.baseLayer !== this) {
                  zoom = this.map.baseLayer.getZoomForResolution(
                      this.getResolutionForZoom(zoom)
                  );
              }
          }
          return zoom;
      }
docs: TRANSLATION: MapObject Zoom <-> OpenLayers Zoom  
  Method: getOLZoomFromMapObjectZoom
  Get the OL zoom index from the map object zoom level
  
  Parameters:
  moZoom - {Integer}
  
  Returns:
  {Integer} An OpenLayers Zoom level, translated from the passed in zoom
  Returns null if null value is passed in