function doZoom(size){
  if(document.getElementById('zoom-area') != null)
    {
      document.getElementById('zoom-area').style.fontSize=size+'px';
      document.getElementById("font-small").className="";
      document.getElementById("font-medium").className="";
      document.getElementById("font-large").className="";
        switch(size)
        {
          case 13 :
            document.getElementById("font-small").className="current";
            break;
          case 18 :
            document.getElementById("font-large").className="current";
            break;
          default :
            document.getElementById("font-medium").className="current";
            break;
        }
    }
  else
    return;  
}