I just saw the guide, thanks, i'll give it a try.
So, suppose that clocks are placed in ##x_1## and ##x_2##, in S they are in sync so,
## \Delta t=0 ##
However in S', which is moving with speed u relative to S, we have for each clock
##t_1'=\gamma(t_1-\frac{u}{c^2}x_1) ##...