function popup_referenzen(Ziel) {
	var Breite = 840;
	var Hoehe = 600;
	
	var Links = (screen.width - Breite)/2;
	var Oben = (screen.height - Hoehe)/2;
	
	void(window.open(Ziel, 'Referenzen', 'width='+Breite+', height='+Hoehe+', left='+Links+', top='+Oben+', scrollbars=yes'));
}