Primary and reciprocal space-time experiments, relativistic reciprocity   relations and Einstein's train-embankment thought experiment
  The concepts of primary and reciprocal experiments and base and travelling frames in special relativity are concisely described and applied to several different space-time experiments. These include Einstein's train/embankment thought experiment and a related thought experiment, due to Sartori, involving two trains in parallel motion with different speeds. Spatially separated clocks which are synchronised in their common proper frame are shown to be so in all inertial frames and their spatial separation to be Lorentz invariant. The interpretions given by Einstein and Sartori of their experiments, as well as those given by the present author in previous papers, are shown to be erroneous. 
J. H. Field