We imagine further that at the two ends A and B of the rod, clocks are placed which synchronize with the clocks of the stationary system, that is to say that their indications correspond at any instant to the "time of the stationary system" at the places where they happen to be. These clocks are therefore "synchronous in the stationary system."
对照示意图，右侧杆a的A端到达位置X时：若静系时钟为8点，则杆a上A钟也为8点（反之，若杆a上A钟为8点，则静系时钟也为8点）；此时左侧杆b的A'端到达X'，此处静系时钟也必然是8点，杆b上A' 钟也是8点。并且，当杆a的A端到达位置X时，B钟和B' 钟也是指向8点的。就是说，只需要“盯住” A, B, A', B' 四只动钟的一只钟，若该钟的读数为8点，则其它钟的读数也为8点——看不看静系的钟都不会有任何影响——因为动钟（盯住一只）与途径地点的静钟，在读数上是一对一之对应关系（按前述蓝色字体描述及（一）的理解），而静系各处的钟是同步的。更形象地，想象杆（不论哪个杆）就是火车，你在火车上睡了一觉醒来看表是6点，此时你就知道火车上其它各处的时钟都是6点，若你看表时火车上某个固定的点恰好经过静系中某位置，则此处（及各处）的静系时钟也是必定6点，而且你的座位可以不是那个固定的点。总之，动钟和静钟的读数是一对一之对应关系，这个对应关系从火车上看还是从静系看，没有分别 —— 就时钟的读数而言。
We imagine further that with each clock there is a moving observer, and that these observers apply to both clocks the criterion established in § 1 for the synchronization of two clocks. Let a ray of light depart from A at the time* tA, let it be reflected at B at the time tB, and reach A again at the time t'A. Taking into consideration the principle of the constancy of the velocity of light we find that
tB - tA =rAB/(c-v) and t'A - tB = rAB/(c+v)
where rAB denotes the length of the moving rod — measured in the stationary system.
Observers moving with the moving rod would thus find that the two clocks were not synchronous, while observers in the stationary system would declare the clocks to be synchronous.
So we see that we cannot attach any absolute signification to the concept of simultaneity, but that two events which, viewed from a system of co-ordinates, are simultaneous, can no longer be looked upon as simultaneous events when envisaged from a system which is in motion relatively to that system.
这个话中的“that system” 就是先前的坐标系（在那里看是同步的），记作A系。envisage 有设想和想象的意思。 “envisaged from a system” 这个system 记作B系，它是相对于A系运动的。好了，A系中看来是同时的事件，在B系中就不能再看作是同时的了。单看原著第2节的这段话，仍然是对的，结论没错。（若作者在静系中实施那个校钟判据，然后从运动的杆上去观测，如何？）。
