Does the "leap second" matter? When updating the atomic clocks, a special committee at the United Nations will decide whether or not it will keep adding an extra second to our clocks. The 'leap second', as it is called, is added every couple of years to keep the clocks accurate. But does it matter? Today presenter Evan Davis talked to Dava Sobel, author of the book Longitude. Sobel said: "For long as people have existed, they have told the time by the sun, which gives us the sense of the day. But those are variable motions and not as exact as the physics of the atom. In recent decades, scientists have preferred to tell atomic time but this doesn't always match. That's when the leap second comes in - and there isn't clear agreement on this point. First broadcast on the BBC's Today Programme on Saturday 3 August.