138 Million years. That's how long it's been since dinosaurs first appeared on Earth. And how long it'll take for this clock to lose a second.
The clock, dubbed the NPL-CsF2 (sexy, right?), is one of an elite class of cesium fountain clocks that's used by Europe, the US, and Japan as the primary frequency standard. This standard is used to obtain an International Atomic Time and Universal Coordinated Time—-both of which are employed in the communications and finance industries as well as for satellite navigation.
It stands just over eight feet tall and tosses cesium-33 atoms through a tunable microwave cavity and measures the number of oscillations as the cesium atoms transition between two energy levels—9,192,631,770 cycles being one second, according to the International System of Units. The external cylinder protects the fountain mechanism from external magnetic fields.
The National Institute of Standards and Technology in the US operates the NIST-F1 cesium fountain, the previous record holder—it only loses a second once every hundred million years or so. As Io9 points out, this loss is due to the fact that "over time, background photons will cause the energy levels in the aluminum ions to shift around a bit, which makes the frequency shift around a bit. Since physicists can't adjust for that variance, they can't maintain the accuracy of the clock."