One clock is fine for keeping track of time. However, it is not very scientific to call what it measures a "Universal Now," because without another clock to compare it to, you have no way of knowing whether the time is universal or not. "Universal Now" implies that everyone everywhere can agree that whatever time is on your one clock could also be the time on all the other synchronised clocks located everyplace else in the universe. You must have at least two synchornised clocks to check whether the time is truly universal by checking whether everyone everywhere can agree that at least those two clocks can be synchronised. It turns out that not everyone agrees that they are synchronised, so the time is not a "Universal Now." If you don't understand what I posted, you should ask a question about it. It is not a quilt or a pattern, it is a clock synchronisation process which shows you how two clocks can be synchronised in one reference frame, but not synchronised in a different reference frame. The key concept is that the speed of light is a constant which is not affected by the motion of the source.