As New Year 2006 arrived around the world, starting in Asia and moving westward around the globe, one second was added to the world's timepieces to make up for a slower Earth rotation.

The new time finally became official when midnight moved across Greenwich Mean Time, the imaginary line through an English observatory town that is the place from where all time zones are measured.

The so-called "leap second" was added by tweaking the atomic clocks, the world's most precise timekeepers that measure time according to the vibrations of caesium-133.

About 330 such timepieces keep track of the day's passage, according to The Independent online - including 100 such clocks in space. But they don't account for natural fluctuations in astronomical movements.

The added second means Saturday night's countdown went like this: 5, 4, 3, 2, 1 and 1.

The leap second was added because atomic clocks tend to run slightly ahead of the Earth's rotation, which is slowing because of the friction of tides raised by the sun and moon. It will be the first extra second added in seven years, Britain's Royal Astronomical
Society said.

Both civilian and military users have come to depend on the ultra-precise time generated by atomic clocks. The US Defence Department's master clock is required to be accurate to less than a billionth of a second per day.

The decision to lengthen 2005 was made by the International Earth Rotation and Reference Systems Service based at the Paris Observatory in France. The practice of adding seconds to selected years began in 1972.

But more seconds may have to be added more rapidly in years to come if Earth, as predicted, slows down its rotation "on a nearly exponential scale", according to Geoff Chester, a spokesperson for the US National Institute of Standards and Technology - the observatory that keeps official US time.