A radio controlled watch periodically synchronizes its quartz oscillator to an atomic clock by receiving a time signal from a transmitting radio station. Some RC watches are capable of receiving just one station, and must be within the coverage area of that station in order to work. Many wristwatches, are now capable of receiving all of the transmitting stations and will synchronize to the signal from the nearest station.
Long established German company Junghans were the pioneers in researching the application of radio controlled technology to wrist watches.
In 1990 they released the Mega 1 the first radio-controlled wristwatch in the world. In addition to its advanced technology this watch also stood out for its futuristic design.
How accurate is a radio controlled watch? The answer is they should always be accurate to within one second of UTC (Coordinated Universal Time), assuming that they synchronize at least every other day and that their quartz oscillator is of reasonable quality.
The key is successful synchronization to a time signal station, because without that advantage an RC watch is just like a run of the mill quartz watch and would lose a second every two days.
The oscillator found inside an RC watch is based on the mechanical vibrations of a quartz crystal, typically counting 32,768 vibrations of the crystal to mark one second.
An atomic clock oscillations are based on the energy transitions of an atom and ‘ticks’ much faster. For example, the second is officially defined internationally as the duration of 9,192,631,770 energy transitions of a 'cesium' atom.
So, in theory, if a Radio-Controlled watch could miraculously be made to run for 20,000,000 years and was somehow able to synchronize once every 24 hours, it would never lose a full second. Such are the benefits of atomic timekeeping.