So here we have a familiar site. Alice is standing in a train moving at speed V while Bob watches from the sidelines. Now on the train is a light clock. Alice measures the length of the light clock and finds it to be L-A. Now I'm going to make a crazy assumption. Perhaps when Bob measures the length of the light clock, he might get a different value which we'll call L-B. Now what are T-A and T-B? The time Alice and Bob measure for a round trip tick of the light clock.