An atomic clock at the UKs National Physical Laboratory (NPL) has the best long-term accuracy of any in the world, research has found. Studies of the clocks performance, to be published in the journal Metrologia, show it is nearly twice as accurate as previously thought. The clock would lose or gain less than a second in some 138 million years. The UK is among the handful of nations providing a standard second that keeps the world on time. However, the international race for higher accuracy is always on, meaning the record may not stand for long. BBC