Actionscript 3 :: Calculating The Current Upload Speed (or Throughput)?

I am uploading files using the upload() method of the FileReference class. I want to display the current connection speed and I was wondering what was a good way to do that.

My current technique is to use a Timer every 1 mili second such as follows:

var speed:Function = function(event:TimerEvent):void {
speed = Math.round((currentBytes - lastBytes) / 1024);
lastBytes = currentBytes;
}
var speedTimer:Timer = new Timer(1000);
speedTimer.addEventListener(TimerEvent.TIMER, uploadSpeed);

and currentBytes gets set into the ProgressEvent.PROGRESS. This technique seems imprecise. I was wondering what other ways I could use to calculate the upload speed while uploading and display it in real time.