Pete's notepad example is instructive.
Clock times stamped on notepads are unambiguous records of clock readings at the time and place of the stamping.
If you run past me holding a note pad, and at the instant you're level with me I reach out and stamp the current time displayed on my watch onto your pad, then you have an unambiguous reading from my watch.
Suppose on the other side of the pad you record the time on your watch at the exact instant I stamp your pad. Suppose you then run off, and after running around in circles for a while you run past me again. Again, I stamp your pad and you write down the time on your watch on the other side. Now you can calculate the differences in accumulated time between our two meetings, as indicated on your watch and on my watch. You have a permanent record which we both agree on.
There are no problems with simultaneity here, since both marks on the pad at the two times are made at the same spatial location. An argument cannot be made that I did not make make stamp simultaneously to your writing on the back of the pad, in either your frame or in my frame. In general, if events A and B occur in the same location at the same time according to one observer, they MUST occur at the same time according to every other observer, regardless of their state of motion.
MacM says above that this is exactly like his argument for "real clock time", but it isn't. Why not? Because in his examples, MacM often compares times as recorded on clock at different spatial locations. In that case, the relativity of simultaneity is very important indeed. If I write on my pad, and you write on yours, how can we guarantee that just because those two events happened at the same time according to my watch, they also happen at the same time according to your watch, when they happened in different places? Answer: we can't.
Clock times stamped on notepads are unambiguous records of clock readings at the time and place of the stamping.
If you run past me holding a note pad, and at the instant you're level with me I reach out and stamp the current time displayed on my watch onto your pad, then you have an unambiguous reading from my watch.
Suppose on the other side of the pad you record the time on your watch at the exact instant I stamp your pad. Suppose you then run off, and after running around in circles for a while you run past me again. Again, I stamp your pad and you write down the time on your watch on the other side. Now you can calculate the differences in accumulated time between our two meetings, as indicated on your watch and on my watch. You have a permanent record which we both agree on.
There are no problems with simultaneity here, since both marks on the pad at the two times are made at the same spatial location. An argument cannot be made that I did not make make stamp simultaneously to your writing on the back of the pad, in either your frame or in my frame. In general, if events A and B occur in the same location at the same time according to one observer, they MUST occur at the same time according to every other observer, regardless of their state of motion.
MacM says above that this is exactly like his argument for "real clock time", but it isn't. Why not? Because in his examples, MacM often compares times as recorded on clock at different spatial locations. In that case, the relativity of simultaneity is very important indeed. If I write on my pad, and you write on yours, how can we guarantee that just because those two events happened at the same time according to my watch, they also happen at the same time according to your watch, when they happened in different places? Answer: we can't.