In the wikipedia page of Lorentz Transformation (http://en.wikipedia.org/wiki/Lorent...ormation_for_frames_in_standard_configuration) it's said that The problem I'm having here is that while taking Lorentz Transformation as true, I failed to verify the statement above, i.e. I can't get "O′ measures O to move at velocity −v along the coincident xx′ axes". Here's my calculation: Is there something wrong with the calculation? Or did I just have a misunderstanding of the statement in wikipedia? Any help will be appreciated!