SL, I am sure all these questions have been asked before and resolved but if we take a look at this next diagram. Please Register or Log in to view the hidden image! It shows a total of 5 objects. According to C object A and C1 are co-moving and objects B and C2 are also co-moving. Object C can ascertain that C1 and C2 are pulsing in phase, in other words they share the same tick rate. He also knows that A and B are also in phase. Object C can clearly see that the same would apply for objects A and B. Now this is where it gets sticky. Object A and object B are unaware of C, C1 and C2. Object A according to SRT will state that object B has all the velocity thus his light pulses on his reflector [remember the two ship scenario posted earlier] will be out of phase. Now clearly there is a conflict between what C knows as true and A and B know as true. The question is : Who is correct? Is C correct? Or is either of A or B correct?