Javascript timer

Hi. Here is code for a simple JavaScript Timer.
My Problem is, that the soconds are junping back to "0" instead of "60,61,62...".

How can modify this code, so that the seconds are not jumping back to "0" after "59".

var zeitintervall	=	null;
var timer		=	null;
function Uhr()
	{
	var Jetzt 	=	new Date(); 
	var myTime 	= 	new Date(Jetzt - StartTime);
	var seconds	=	myTime.getSeconds();
	if(seconds < 10){ seconds = "0"+seconds; }
	var millis	=	myTime.getMilliseconds().toString();
	document.getElementById('counter').innerHTML = seconds + ':' + millis.substr(0,2);
	timer=setTimeout("Uhr()", 20);
	zeitintervall = myTime;
	}
function StartStop(){
		StartTime 	= 	new Date();
		timer		=	setTimeout("Uhr()", 20);
	}

PHP:

 

Try not to use the Date( ) object, and just manually count

 

But i need the milliseconds...

 

Replace
var seconds = myTime.getSeconds();

With
var seconds = myTime.getHours()*3600 + myTime.getMinutes()*60 + myTime.getSeconds();

There may be a better way of doing it, I'm still learning this stuff