public Date getCounterStartTime() {		
		if (counterList.size() == 0)
			return null;
		Date date = counterList.get(0).getStartTime();
		for (int i = 1; i <counterList.size(); ++i) {
			Date date1 = counterList.get(i).getStartTime();
			if (date1 != null && date1.compareTo(date) < 0)
				date = date1;
		}
		return (Date) date.clone();	
	}