[hnbear]

In industries like finance each datacenter will have its own GPS receivers with dedicated antennae, and custom timekeeping devices to act as the local stratum-1 servers, and use PTP. Within the DC servers will have very low jitter and high bandwidth network routes to ensure tight accuracy, typically over different networks than the high-traffic connectivity, eg. different interfaces. Where you really really care you can further optimize the OS to ensure tight timekeeping.

Industries that care aren’t sourcing time across residential ISP links and consumer NTP sources. But, for most people it’s accurate enough.