code: def elapsed_time(self):
          
          td = (datetime.datetime.now() - self.start_time)
  
          sec = td.seconds
          ms = int(td.microseconds / 1000)
          return '{:02}:{:02}.{:03}'.format(sec % 3600 // 60, sec % 60, ms)
docs: Return elapsed time as min:sec:ms.  The .split separates out the
          millisecond