function ShowAdventskalender() { 
	var PopupWidth  = 640;
	var PopupHeight = 480;
	var PopupLeft   = Math.floor((screen.availWidth / 2) - PopupWidth / 2);
	var PopupTop    = Math.floor((screen.availHeight / 2) - PopupHeight / 2);

	popup = window.open(
		'',
		'Adventskalender',
		'fullscreen=0, toolbar=no, location=no,directories=no, status=no, menubar=no, scrollbars=yes, resizable=no, width=' + PopupWidth + ', height=' + PopupHeight + ', top=' + PopupTop + ', left=' + PopupLeft
	);
	popup.resizeTo(PopupWidth,PopupHeight);
	popup.moveTo(PopupLeft,PopupTop);
	popup.location = 'adventskalender.php';
}