So what we do is we pick an origin, call it zero, we put some markers there to measure distance, and we say this guy is sitting at 1,2,3,4,5.

我们现在选择一个原点,称其为零点,我们做一些标记来测量距离,这个点在五个单位长度的地方

耶鲁公开课 - 基础物理课程节选