I installed a master clock system in a insurance company building about 8 years ago.
It was nothing like the old master clock system.
It has Large LED displays and is controlled via it's own LAN (Local Area Network)
It was a nice system and it could be interconnected with other building systems like the fire alarm so the display would change from the time to flashing "FIRE".
Anyway I doubt we will see that type of master clock system in the future as 'controlled' clocks are cheap and easy.
Beside me on the wall now is a Analog clock that once an hour verifies the time via radio signal from NIST in Colorado USA.
WWVB atomic clock receiver
A radio system is available in North America set up and operated by NIST - the National Institute of Standards and Technology, located in Fort Collins, Colorado. NIST operates radio station WWVB, which is the station that transmits the time codes. WWVB has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from WWVB a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America. The time codes are sent from WWVB using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: • 0.2 seconds of reduced power means a binary zero • 0.5 seconds of reduced power is a binary one. • 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years. The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock's time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.
I think my clock cost less than $20.00 and no wiring was needed.