. There are other synchronization conventions like slow clock transport, just as arbitrary as Einstein's, but having the property that the value of the one-way speed of light according to them is an empirical property of the universe, not just a trivial consequence of our definition.  The key to Einsteins theory is his Light Postulate. As I understand it, he based it on emperical evidence, Michaelson et al. OK?  Abstract discussions of what time is, in a philosophical sense, really belong in the philosophy forum.  Meanwhile, science can tell us a lot of usefull things about how clocks behave - and about how the seasons behave as well - because it's about things we can actually measure, and questions can actually be settled by pointing to experiment, rather than debated without end and without any resolution.  I hadnt intended a philosopical discussion. But rather an attempt to understand Einsteins relativity. He places clocks in his two frames without stating basis or calibration ( re day, no.of seconds per day). There has resulted endless debate about the relation of the two sets of clocks. My conclusion that the time of the moving frame is assigned, and that the everyday time of the moving frame has no bearing ( when viewing from the stationary frame ) seems to me to resolve these discussions. If clocks are man made, what does science say about their behavior?  I hadnt intended a philosopical discussion. But rather an attempt to understand Einsteins relativity. He places clocks in his two frames without stating basis or calibration ( re day, no.of seconds per day). There has resulted endless debate about the relation of the two sets of clocks. My conclusion that the time of the moving frame is assigned, and that the everyday time of the moving frame has no bearing ( when viewing from the stationary frame ) seems to me to resolve these discussions. If clocks are man made, what does science say about their behavior?  If you want to understand Einstein's Special Relativity, you need to accept the answers that you are given by people who already understand it instead of putting up resistance to them.  