This is a collection of pictures of rather weird and wonderful clocks called "atomic clocks". These clocks keep the most accurate time on earth. Most atomic clocks operate by counting the number of oscillations of vapourised caesium atoms in an electromagnetic field. One second is equivalent to 9,192,631,770 oscillations. Currently the world's most accurate clock is the CS2 atomic clock at the German National Standards Laboratory, near Hanover, Germany. It loses only 3 billionths of a second a day. But there is now an even more accurate atomic clock, the NIST-7, which will be accurate to one billionth of a second a day. This means in three million years it will lose only a single second.