The precise measurement of time and time interval is a key enabler of modern technology in which a profusion of electronic devices and communications equipments depend on the synchronization of time and frequency in order to operate properly over distances of thousands of miles or more. Cell phones, mobile phones, the Internet, and satellite navigation, among other ubiquitous consumer services, all depend on clocks and oscillators that control their operation. Universal access by these and related services to a standardized reference time has benefited from the establishment in 1970 of a time scale called Coordinated Universal Time (UTC), and by the means to maintain that time scale both nationally and internationally.