code: public Duration convertUnits(TimeUnit type, ProjectProperties defaults)
     {
        return (convertUnits(m_duration, m_units, type, defaults));
     }
docs: This method provides an <i>approximate</i> conversion between duration
  units. It does take into account the project defaults for number of hours
  in a day and a week, but it does not take account of calendar details.
  The results obtained from it should therefore be treated with caution.
  
  @param type target duration type
  @param defaults project properties containing default values
  @return new Duration instance