LONDON, Dec. 30 (Xinhua) -- Thousands of people will gaze up at London's famous Big Ben to wait for the famous Westminster chimes to ring in the new year.
But on Saturday night, the celebrations may be premature, by just a second.
The traditional 10-second countdown will take 11 seconds this year, as Big Ben accommodates what is a leap second in world timing.
So precise are atomic clocks that even a micro-second really does count for timekeepers around the world. Sophisticated, hi-tech devices are used to ensure that atomic clocks all keep perfect timing.
At Big Ben, clock-keepers have no such space-age technology to ensure the famous clock is in tune with the rest of the world.Instead they use a stack of old pennies to accurately balance the clock mechanism.
Big Ben clock keeper Steve Jaggs has already placed an old penny on the mechanism.
He ascended the tower on Friday to check to make sure the mechanism is keeping perfect time.
"Adding an old penny speeds up the clock by 2/5 of a second over 24 hours so it might take four pennies to increase the time by a second."
The pennies ought to ensure that as 2016 ends and the new year arrives, Big Ben will have resolved the leap-second issue.
Leap seconds are introduced because the rotation of the earth is slowing. It was only the introduction of super-accurate atomic clocks that made timing a far more precise science.
In Britain, the country's time-standard is set by the National Physical Laboratory (NPL). This year will be the 27th leap second to be introduced, the last on New Year's Eve in 2008.
A spokesman for the NPL, based at Teddington near London, said: "The atomic clocks housed at NPL are nearly a million times better at keeping time than the rotation of the earth. Leap seconds are used to provide a link between the extremely stable time scale based on atomic clocks and the more variable time scale of the solar day.
"A leap second is added to Coordinated Universal Time (UTC) when the earth's rotation becomes out of sync with the time kept by the atomic clocks held at national measurement institutes such as NPL. When time based on the earth's rotation lags behind UTC, a second is added to the atomic time scale. It is also possible for a second to be removed from the UTC time scale, although such a negative leap second has never been required."
A decision as to whether a leap second is required is taken by the Earth Orientation Center of the International Earth Rotation and Reference Systems Service(IERS), approximately six months in advance.
Peter Whibberley, senior research scientist in the Time and Frequency Group at NPL, said: "Atomic clocks are more than a million times better at keeping time than the rotation of the Earth, which fluctuates unpredictably."
"Leap seconds are needed to prevent civil time drifting away from Earth time. Although the drift is small -- taking around a thousand years to accumulate a one-hour difference -- if not corrected, it would eventually result in clocks showing midday before sunrise. "
