protected String computeAggregateMean(Map unitToNumAssets, Map unitToMean) {
protected String computeAggregateMean(Logger l, Map unitToNumAssets, Map unitToMean) {
  protected String computeAggregateMean(Map unitToNumAssets, Map unitToMean) {    String retval = null;    long sum = 0;    long totalAssets = 0;    try {      for (Iterator iter = unitToMean.keySet().iterator(); iter.hasNext();) {	String unit = (String) iter.next();	int unitNumAssets = ((Integer) unitToNumAssets.get(unit)).intValue();	String unitArrivalMean = (String) unitToMean.get(unit);	long meanL = format.parse(unitArrivalMean).getTime();	sum += unitNumAssets * meanL;	totalAssets += unitNumAssets;      }      retval = format.format(new Date((long)(sum / totalAssets)));    } catch (ParseException e) {      System.err.println ("ArrivalTimePrecisionTest.computeAggregateMean() - could not parse date format.");    }    return retval;  }