dynamic graphs (in real time)

I'm writing an application that reads data from some serial sensor. I'd like to generate a graph (I'm using the jpgraph) from that data and display it in real time. The question is: how can I show data while they're changing ? I've tried to reload the browser each seconds, but it's not so elegant (I don't want to reload the entire page) and I need to display data more frequently. Some ideas? Carlo