code: @Deprecated public Duration getDuration(Date startDate, Date endDate) throws MPXJException
     {
        return (getDuration("Standard", startDate, endDate));
     }
docs: This method is used to calculate the duration of work between two fixed
  dates according to the work schedule defined in the named calendar. The
  calendar used is the "Standard" calendar. If this calendar does not exist,
  and exception will be thrown.
  
  @param startDate start of the period
  @param endDate end of the period
  @return new Duration object
  @throws MPXJException normally when no Standard calendar is available
  @deprecated use calendar.getDuration(startDate, endDate)