Standard time and frequency signal

standard time and frequency signal service (STFS): In the United States, standard time and frequency signals, 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).

Note: The Radio Regulations (RR) define an identical international service as standard frequency and time signal service .

Source: from Federal Standard 1037C