Disclaimer: I've been involved in supporting the NTP Public Services Project since 2003. I assure you, with the right hardware and paying attention to your lat

Disclaimer: I've been involved in supporting the NTP Public Services Project since 2003. I assure you, with the right hardware and paying attention to your latencies, NTP can get you down below one millisecond accuracy. Poul Henning Kamp was doing nanosecond level accuracy with NTP back in the mid-aughts, but then he had rewritten the NTP server code, the NTP client code, and the kernel on the server. As an NTP service provider, what you really want to keep an eye on is the Clock Error Bound that gives you the worst case estimate for how bad the time is that you could be serving to your customers. For the client side, you mainly care about just the accuracy you're actually getting.