An atomic radio clock and a GPS clock are both devices that repeatedly check the time with an information source via a radio connection. This means the user should not need to repeatedly alter the clock to correct for any errors. The references to "radio" are purely to do with the time checking and are nothing to do with any audio radio receivers that may be part of the device.
Mechanical watches and clocks can become inaccurate in the long run. There are several causes for this, one of which is that gravity can affect moving parts. According to a February 2009 article in Digital Journal, a standard wristwatch can begin running 15 seconds slow after a month. Radio clocks work by checking a trusted accurate time source at regular intervals and automatically correcting themselves if there is any disparity.
Both atomic radio clocks and GPS clocks take their time signals from an atomic clock. An atomic clock is a device used to provide synchronization signals for people and organizations across a country or region. It works by tracking rises and falls in the radiation levels of atoms of a material called caesium, a characteristic that can be isolated and is extremely predictable and consistent. Atomic clocks are used around the world as an "official" time signal. The consistency of atomic clocks allows all countries in the world to follow a consistent time, something that is vital for activities such as tracking when a specific transaction took place on financial markets.
Atomic Radio Clock
Most facilities that house an atomic clock broadcast a series of signals on a dedicated frequency telling the current time based on the atomic clock. An atomic radio clock is a consumer device that checks that its time reading is correct by monitoring this frequency for time signals. Most atomic radio clocks can use this information to ensure an accuracy of up to one-hundredth of a second. This may be limited if the clock is too far away from a radio broadcast to receive an ideal signal strength, if it doesn't have a clear line of sight to the signal, or if it is affected by unfavorable atmospheric conditions.
A GPS clock uses a similar principle to an atomic radio clock. However, rather than get signals from terrestrial radio broadcasts, it receives signals from the same GPS satellites that are more commonly used for location tracking. The clock then combines the time broadcast by the satellites with terrestrial broadcasts that detail any potential errors that arise as the signals travels from space to Earth.
The main advantage of a GPS clock is that it will be able to get signals from multiple satellites, reducing the effects of any inaccuracies caused by limitations to reception. Whether it is worth getting a GPS clock depends on precisely what degree of accuracy you need. For ordinary consumer use, where the main aim is to avoid the inconvenience of having to correct a clock that "loses time," an atomic radio clock is likely to be sufficient. A GPS clock is more suited to people who need an extremely high degree of accuracy and reliability.
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