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Panoramic view of the clock hall at PTB with the four caesium clocks CS1, CS2, CSF1 and CSF2.

Is time information also available online?

For the synchronization of computer clocks via Internet PTB offers three time servers. These servers use the "network time protocol" (NTP) to disseminate the time information. This protocol was designed with the aim of synchronizing computers within local networks and in wide-area networks. The protocol is based on the IP protocol used in the Internet, is available for all relevant operating systems and has been pre-installed in most PCs and mobile devices.


scheme of the NTP time server of the PTB

The use of the time servers of PTB for the synchronization of a computer requires a program supporting this protocol. Such programs are available for the operating systems Windows, Linux, macOS, and others. A list of suitable programs can be found on the web pages of our US partner institute NIST

After installation of such a program, the addresses of the NTP servers to be included in the synchronization must be added. The following addresses must be entered to use the time servers of PTB for synchronization:






The operation and supervision of the time servers are in the responsibility of the PTB Section Q.42 IP-Based Dissemination of Time. It is intended to make at least one of the three time servers permanently available. PTB, however, has no influence on problems during transmission and time errors due to delays in the Internet.

Under the number +49 531 51 20 38 PTB offers time information via the public telephone network. Via telephone modems, computers and data acquisition systems have automatic access to exact time information.