Here you can see working example. Pretty good solution http://www.wattnotions.com/making-updating-graph-using-javascript-jpgraph/
The main idea is summarizing from "Rizwan Shamsher Kaim Khani" and official doc http://jpgraph.net/download/manuals/chunkhtml/ch05s05.html
If you very simplify code, you can get very short js code into your HTML. php file remains as it is.
<!DOCTYPE html>
<html>
<body>
<script>
function refresh() {
setInterval(function() {
var image = document.getElementById('myImage');
image.src = "index.php?" + new Date().getTime();
}, 1000);
}
refresh();
</script>
<img id="myImage" src="index.php"/>
</body>
</html>
To see refresh tries realtime add this into your index.php */
/* NOTE! $today variable is mandatory usage */
$today = date("Y-m-d H:i:s");
$graph->title->Set('Title'.' '.$today);