Hi SitePoint

I'm not having any luck with stopping an Ajax.PeriodicalUpdater function, Prototype 1.5.0. My function looks like this and I call it on window.onload:

function fileuploadStatus() {
var u = new Ajax.PeriodicalUpdater( 'statusDisplay', 'returnStatus.lasso', { method: 'get', parameters: 'fw_s=sid', frequency: 2 } );
When I read the documentation on http://www.prototypejs.org/api/ajax/periodicalUpdater I get the impression I should be able to call fileuploadStatus.stop() - for example in a link like this:
<a href="#" onclick="fileuploadStatus.stop();">stop</a> but it doesn't work, I get "stop is not a function" back from the browser debugger.

I'm missing something obvious here - can somebody enlighten me?