function cal_update(formdata)
{
  var cal_int = 'http://www.google.com/calendar/embed?showTitle=0&height=500&wkst=2&ctz=Europe%2FBerlin&hl=de&bgcolor=%23FFFFFF';

  if(formdata.cal_akku.checked)
    cal_int = cal_int + '&src=uatum0nljqc839qpp2csm27has%40group.calendar.google.com&color=%23528800';
  if(formdata.cal_buha.checked)
    cal_int = cal_int + '&src=barsbuettelbuergerhaus%40googlemail.com&color=%232952A3';
  if(formdata.cal_buve.checked)
    cal_int = cal_int + '&src=arlhjflac4rt2cf42jegb5l8r0%40group.calendar.google.com&color=%238D6F47';

  this.document.getElementById('cal_google').src = cal_int;
  return false;
}