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Network Time Protocol

Network Time Protocol (NTP) is an Internet standard protocol which enables client computers to maintain system time synchronization to the US Naval Observatory Master Clocks in Washington, DC and Colorado Springs, CO.
NTP runs as a client program on a computer. It sends periodic time requests to one or more servers, obtaining server time stamps and using them to adjust the client's clock.
Typical accuracy achieved is in the range 1 - 30 ms continuous, and is highly dependent on the symmetry and speed of the Internet path between client and server. Best results are achieved using a combination of servers which are closest to the client in a network sense.
To obtain precise time from USNO NTP servers, follow these procedures:
1. Download NTP client software from 
2. Select one or more NTP servers and add to your client configuration.
3. Run the NTP client on your machine. We request that you allow no more than three of your clients to poll our servers directly. Organizations with many clients should obtain time from local stratum 2 servers. ISPs should configure routers or firewalls to serve as stratum 2 servers to the ISP network. Dial-in clients should contact your ISP for information about NTP services.
NTP Servers
All of the following stratum 1 NTP servers are open to stratum 2 servers within the same time zone and to others by arrangement. Individual users should consult the public list of stratum 2 servers.
Please note that these servers support the Network Time Protocol (Internet RFC-1305a, RFC-5905) and Simple Network Time Protocol (SNTP), as provided by  NTP and Chrony software.

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