The access-control, intrusion-detection and camera systems keep synchronised clocks, by automatic or manual means, so that their timestamps never drift more than one minute apart. In particular: manual synchronisation takes place at least every quarter, and the synchronisation events and any variances are recorded, with the records retained for a year or longer.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.