public void add(String value)
	{
		if(counter >= 0) {
			try {
				if(value != null) {
					double doubleValue = format.parse(value).doubleValue();
					sum += doubleValue;
					
					if((doubleValue < min) || (counter == 0)) {
						min = doubleValue;
					}
					
					if((doubleValue > max) || (counter == 0)) {
						max = doubleValue;
					}
				}
				// else: tread it as zero
				counter++;
			}
			catch(Exception excDou) {
				// there was one entry, which is not a number
				// -> mark it as invalid
				counter = -1;
			}
		}
	}