Abstract :
High-speed electronics require clocks that must be calibrated to precise standards. Once, the ultimate standard was based on astronomical observations. But in the mid- 1950s, the first reliable atomic clocks were constructed and enthusiastically adopted: This ad for a portable atomic clock??? weighing only 14 kilograms and with an 8-hour battery life??? was published in April 1967, the same year the second was redefined in terms of the electronic transitions of a cesium atom. But atomic clocks didn???t really get much more portable than this until 2011, following a breakthrough that squeezed an atomic clock down to the size of a computer chip???leading to, among other things, the world???s first atomic pocket watch.
