Synchronise your computer with NPL's atomic clock
How does a computer know the time and date? How does it know when the clocks are next due to go forward or back? Or when there will next be 61 seconds in the minute?
A computer time-stamps every event, such as an e-mail being sent or a file saved, by taking the time from its internal clock. This clock is usually an inexpensive quartz oscillator that can drift by several seconds over a day and gradually build up an error of many minutes. If the computer is to tell the time accurately it must set its internal clock regularly against a trusted external source of time, which must be both accurate and reliable. NPL offers two services that provide access to just such a source - the UK national time scale located at NPL, which is based on a group of atomic clocks.
- The Telephone Time Service (TTS) allows a computer to set its internal clock by direct telephone connection to a server at NPL. A call to the NPL TTS can be made at any time of the day or night, and it allows a computer equipped with a suitable modem and software to set its clock to UK local time and to learn in advance about important time changes. It is particularly valuable in situations where the computer is not connected to the Internet, for example in a security system where the equipment needs to be tamper-proof, or where a reliable source of UK local time is required. A User's Guide to the NPL Telephone Time Service is available that explains how to obtain and install software that will allow a computer to use the service, and includes a full description of the time code for anyone wishing to write their own software to access the service. It can be downloaded here (free of charge)
- The Internet Time Service (ITS) allows a computer to set its internal clock by connecting over the Internet to a server at NPL that transmits a time code using the well-established Network Time Protocol (NTP). Either a dial-up or broadband Internet connection can be used. A User's Guide to the NPL Internet Time Service provides more information and explains how to obtain and install software that will allow a computer to use the service. It can be downloaded here (free of charge)
The two services are complementary; the differences between them are summarised in the table below.
| Telephone Time Service | Internet Time Service | |
| Means of access | Modem connected to external telephone line | Internet service provider |
| Phone number/ Internet addresses |
0906 851 6333 | ntp1.npl.co.uk ntp2.npl.co.uk |
| Availability | Within the UK | Worldwide |
| Cost | Approx. 20p per call | Free |
| Time reference | UK civil time (UTC or BST) | UTC |
| Accuracy | Around 30 ms | Around 20 ms |
| Software | NPL Phoneclock for Windows PCs | Widely available |
| User Guide | TTS User Guide |
ITS User Guide |
Software for the Telephone Time Service
A program called 'NPL Phoneclock' has been produced by NPL for use with the NPL Telephone Time Service. NPL Phoneclock is intended for use on PCs running most current versions of the Microsoft Windows operating system. It is compatible with Windows NT, 95, 98 and 2000, and will normally run under Windows XP. NPL Phoneclock can be downloaded here (free of charge).
Contact
Customer Services tel: +44 20 8943 6796
E-mail: timefreq_enquiries@npl.co.uk