code: @Nonnull
    public EChange stop ()
    {
      // Already stopped?
      if (m_nStartDT == 0)
        return EChange.UNCHANGED;
  
      final long nCurrentNanoTime = getCurrentNanoTime ();
      m_nDurationNanos += (nCurrentNanoTime - m_nStartDT);
      m_nStartDT = 0;
      return EChange.CHANGED;
    }
docs: Stop the stop watch.
  
  @return {@link EChange#CHANGED} if the stop watch was previously running
  and is now stopped, and {@link EChange#UNCHANGED} if the stop watch
  was already stopped.