A small limitation is that a trace relationship is not allowed to be circular.
其中有一条很小的限制条件，那就是追溯的关系不允许是闭环的。
2
Then, as the sky darkened, the stars became visible, the Earth’s spin making them trace their own circular paths about the north and south celestial poles.
随后，天色渐黑，星空依稀可见，地球的自转使得恒星在南天极和北天极沿着个子的轨道划下绚丽光环。
3
In this paper, discussed the vibration of circular parts machining, proposed out the best trace of CNC powerful turning and the method of limited depth.