Hello, again, lately i've been going over special relativity again and have decided to finally look into the light clock thought experiment to see how he derived time dilation. Of course, it was going well until I checked wikipedia, I know not the best source, for how it was supposed to go and one part got me confused. Please Register or Log in to view the hidden image! How did it get from step two to step three without cancelling out the time signatures. Did I miss some elementary math trick or what, it bewilders me. Also, what is the benefit of the +--- and -+++ sign conventions in the Minkowski metric? The later makes time imaginary and I happen to find it unnecessary as well as unusable but maybe i'm just a bit clueless on how it is applied. More posts and questions will follow.