National Physical Laboratory

Why do we need accurate time?

Time in everyday life

Everyone needs to know what the time is at some point in the day, whether to catch our bus in the morning or to celebrate the New Year at the right moment. For this sort of timekeeping, our personal watches and household clocks are accurate enough. A typical quartz clock, for example, manages to keep time to within a second over ten days.

When it comes to sending data down a phone line or navigating by satellites, however, we need as much precision as possible.

Time and technology

Applications from global communications to satellite navigation, surveying and transport systems are underpinned by precise timing, and the same stable and accurate time scale must be in use everywhere for such systems to operate correctly.

Telecommunications rely on accurate timing to ensure that the switches routing digital signals through networks all run at the same rate. If they did not, those switches running slow would not be able to cope with the traffic and messages would be lost. When speaking on the telephone, you might hear a click or a crackle if just one data packet was lost. If sending a fax, a line might be smeared. If communicating over the internet, the connection might be lost completely. As we become more reliant on the telephone and the internet, we are also becoming more dependent on atomic clock time.

For the navigation of ships, aeroplanes, and more recently family cars, Global Positioning System (GPS) satellites that orbit the Earth broadcast timing signals from their atomic clocks. By looking at the signal from four (or more) satellites, the user's position can be determined. The time has to be incredibly accurate as light travels 30 centimetres in one nanosecond (or 300 million metres in one second!) so that any tiny error in the time signal could put you off course by a very long way. The GPS system has proved particularly effective during sea rescue operations and in situations such as Arctic expeditions where navigating by traditional landmarks and signposts is impossible.

Where does the time come from?

There is no single master clock for the world. Instead, the international time standard is maintained by around 70 time laboratories around the world and is based on the average of some 400 atomic clocks. That diversity provides both safety (for example, a single clock in an earthquake zone would not be a good idea) and accessibility (each major industrial nation contributes to the time standard, and hence has direct access to the atomic clocks).

In the UK, it is the National Physical Laboratory that maintains and develops the national time standard. The group of atomic clocks at NPL keep the UK's time accurate to within four billionths of a second, which means that the error in a day or a week is tiny.

Time worldwide

The international time standard, held by NPL and the other time laboratories, is made freely available by radio broadcasts. The MSF signal was transmitted from Rugby Radio Station in Warwickshire from 1950 to 2007. Since 1 April 2007, the Anthorn Radio Station has broadcast a time signal covering the whole of the UK, based on NPL's atomic clocks.

This time signal has a number of applications. When you call the speaking clock, or hear the time 'pips' on the radio, they will have got the time from the NPL atomic clocks. The Global Positioning System gets its time from the US Naval Observatory in Washington, which in turn gets its time, like NPL, from participating in the international time standard.

Those time signals are not only accurate, but are also very reliable. Systems around Britain and beyond that rely on accurate timekeeping have access to this signal so that processes such as telephone conversations and internet surfing operate smoothly. This time is compared with other clocks around the world so that everyone uses the same time system. Navigating between countries would be much more complicated without this co-operation.

Last Updated: 30 Jan 2014
Created: 26 Oct 2011

Registration

Please note that the information will not be divulged to third parties, or used without your permission

Login