The pendulum of this mid-century beauty is made of the alloy ... With access to a 10-MHz timebase from a cesium fountain atomic clock — no less a clock than the one that’s used to define ...

But that changed with the invention of atomic clocks in the mid-20th century; scientists then decided to base the second on the natural vibrations of the cesium atom. [How to Build the Most ...

The quest to create the perfect scientific timepiece has led to the development of an atomic clock that researchers from JILA claim to be fifty percent more accurate than results reported last year.