Atomic Clocks that consumers buy are really radio-controlled clocks; they are just called atomic clocks by the manufactures. They are controlled by a radio signal from the (NIST) National Institute of Standards and Technology's atomic clock in Colorado and Hawaii. This US government department provides world’s most accurate radio time signals for free to the citizens of the USA. This radio signal synchronizes these clocks with the official US time. The clocks are normal clocks except they have a radio receiver, which adjust them a few times per day to the NIST official US time. The big advantage of these clocks it that they are always right. However if you take them outside of the USA they just function as normal clocks. A true Atomic Clock requires a lab full of engineers to operate and is not affordable to the average person.