Thanks prof, i follow all the steps the you explain in your last post, and slider work but it's normal that space between trace and other not be equal, i tried to make the space between
each trace and the other be equal for applet be more simple, for example if we have 3 diffrent tracks what i tried to do is be space between the three trace be equal slider move satellite normal, but when i move satellite to other postion using slider the space of the trace old and the new Trace that follow satellite not be equal, be diffrent, i really need to when change satellite to diffrent postion space be equal between all traces.
i really need help  in this point too, i also attach the XML file to you can watch what i add.
PS: I'm not sure the slider if work completely right or no.
Thanks,