i have a video player and i need to detect when the scrubber is more then 20.6% across this is the script i got so far

function ad()
	{
		if (document.getElementById('scrubber').style.left > "20.6%") 
		{
			document.getElementById('ad').style.display = 'block'
		}else{
		setTimeout(ad(),1000);
		}
	}

this is the scrubber and the ad i need to show when the scrubber is past 20.6%

<a id="scrubber" href="#" class="scrubber-button" style="left: 0%;"><img src="scrubber.gif" width="16" height="16"></a>

<div id="ad" class="ad" style="display:none;">Ad This is the ad if you see this then i win.</div>