Appendix 1 - simple Lorentz transformation derivation found at - http://www.bartleby.com/173/a1.html Given in equation (3) (x'-ct') = Y(x-ct) [Y = const.] by rearrangement, it yields, (x'-ct')/(x-ct) = Y. But it is stated that both (x-ct) and (x'-ct') are zero, so we have "zero over zero" - a mathematical no-no. There is surely no way something so trivial could of been over-looked when proof-reading, so I ask where it is I am going wrong in this derivation? Also, is it such the case when considering the 3D model? Many thanks.