var w=786;                        /* popup window width*/
  var h=536;                        /* popup window height*/

  var l=(screen.width-w)/2;         /*this centers horizontally*/
  var t=(screen.height-h)/2;        /*this centers vertically*/

  var url="chart.php";

  var features="left="+l+",top="+t+",width="+w+",height="+h+",scrollbars=auto";

function popItUp() { 
     window.open(url,"",features);
 }