Standard time and frequency signal
The Standard Time and Frequency Signal (STFS) is a Radiocommunication service providing the transmission of specified frequency and time signal, of stated high precision, intended for general reception in the United States and beyond. The radio signals are broadcast on very precise carrier frequencies by the U.S. Naval Observatory and the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS). The technical specification of that particular service is in line to the provisions of the International Telecommunication Union´s (ITU) Radio Regulations (RR)
A similar service is operated in the United Kingdom by the National Physical Laboratory, broadcasting from Anthorn radio station in north-west England, and by the BBC using the 198 kHz carrier of the Radio 4 national radio station with a frequency accuracy of 1 part in 1011.
...
Wikipedia