The evolution of time measurement, Part 5: radio controlled clocks [Recalibration]

Frustrating as it is to time metrologists, a group of independent clocks can't keep the exact same time. To prove this, synchronize a group of wristwatches and then check them again a month later. You'll likely find that they disagree with each other by at least a few seconds. If you attempt the same exercise with a group of cesium clocks, the time differences will be tiny, nanoseconds instead of seconds, but again, the clocks won't keep the exact same time. The British horologist Frank Hope-Jones recognized these problems more than a century ago and became an advocate for collectivism, rather than individualism in clocks. The clocks of Hope-Jones' era were typically self-wound, were synchronized from different sources, and ran at very different rates. Therefore, none of them would come close to agreeing with the others.