function open_print_scherm(pagina, breedte, hoogte) 
{ 
	var marge_links = (screen.availWidth - breedte) / 2; 
	var marge_boven = (screen.availHeight - hoogte) / 2; 

	nieuw_venster = window.open(pagina,'','width=0,height=0,scrollbars=no,resizable=no,status=no,toolbar=no,menubar=no,screenX=' + marge_links + ',screenY=' + marge_boven + ',left=' + marge_links + ',top=' + marge_boven + ''); 
}