Internal function that is run in a separate thread. Do not call 
		directly.

def __run(self):
		""" Internal function that is run in a separate thread. Do not call 
		directly. """
		self.interval_start = time.time()
		while self.status != STOPPED:
			if self.status == RUNNING:
				self.current_interval_duration = time.time() - self.interval_start

			# If max_duration is set, stop the clock if it is reached
			if self.max_duration and self.time > self.max_duration:
				self.status == STOPPED

			# One refresh per millisecond seems enough
			time.sleep(0.001)