code: public Note getNoteFirstExtendedLineLow() {
  		if (m_lowNote == null) {
  			//A 7th (label=6) for 5 lines,
  			//A 5th (label=4) for 3 lines,
  			//A 3rd (label=2) for 1 line
  			byte label = (byte) (getStaffLines() + 1);
  			Interval interv = new Interval(label,
  				label==5?Interval.PERFECT:Interval.MAJOR,
  				Interval.DOWNWARD);
  			m_lowNote = interv.calculateSecondNote(getMiddleNote());
  			m_lowNote.setAccidental(new Accidental());//Accidental.NONE
  		}
  		return m_lowNote;
  	}
docs: Return the low first note which needs an extended staff line.
  <BR>For a 5 lines staff, it's a seventh under the middle note.
  For standard treble G clef, returns <TT>C</TT>.