Also Einstein (1917) created a model with an observer in the middle between A and B. However, in his description two signals are sent from A and B to the observer.
爱因斯坦与1917年也建立了一个类似的模型：他也在时钟A、B中间放置了一个观测者，不同的是他描述的是有两个信号分别从A和B发给观测者。