Pygame FPS 比我想要的快

Pygame FPS faster than what I want

我正在尝试 运行 以 80 帧/秒的速度运行游戏,但我得到的是 83 帧/秒?!怎么回事?

while 1:
  start = time()
  clock.tick_busy_loop(80)
  self.update()
  fps=int(1./(time()-start))
  print fps, 'fps'
>> 83 fps
Resolution of pygame clock = 1 msec
80 fps = 12.5 msec
83 fps = 12 msec
int(12.5) = 12