They call these battery Atomic Clocks, but in fact they are digital quartz clocks that take their time from the NIST, or one of the number of other time standard services. The correct name would be a "Radio Synchronized Clock", and NOT an Atomic Clock. The average person would never have the funds, and or resources to purchase and maintain a real atomic clock!
The clock has to be first set up to the proper time zone, and put in the mode to receive the time exteraly. The instruction manual should have the details for the particular model.
In a store environment as like in a shopping plaza or department store, with all the lighting, concrete walls, and etc, the signal that it must receive must be highly reduced. At home where the receipton of outside signals are much better, the clock should work normaly. The instruction manual should give the details of how to properly set it up.
As a vendor, I would think it is bad sales practice to have the clocks all being off time to each other. I would have taken the time to set them properly, and then to have the necessary information about them posted. But, this is their problem.
The principle of the clock is that it uses a receiver with a decoder that can decode the time that is sent on the carrier of the NIST station, or the service being used. There are a number of frequencies being used, and the receiver has a system that can scan for the best one. The reception is effected by the atmospheric probagation factors. Shortwave listeners and amature radio operators would be familiar with this. At different times of the day, and under different atmospheric conditions, radio reception will be affected.
When the clock is receiving the NIST signal it keeps itself synchronized to the time signal. When the signal dissapears, the clock will free-run just like any quartz standard clock.
The average accuracy of the clock is dependent on the quality of design, and the reception of the serviced signal. Most of the consumer quartz clocks and watches will keep an accuracy of about 5 to
10 seconds per month. This is for a standard free running quartz clock or watch. There are some very expensive wathes and clocks that can do a bit better. With a radio synchronized clock, the time should be more accurate, because of the periodic corrections during the coarse of each day.
The only error that these clocks will have is their total internal delay, and the time it takes for the signal to reach, and be processed in the clock. This is most likely in the micro-second range of error.
The general trend of many of the manufactures is to start making these clocks the main stream of clocks. This type of clock will be more common on the market over the next number of years. There are also a number of watches coming out with this feature. There are some places where this type of time keeping is now the main stream.
With all of this, I am still late for work at times...
Jerry Greenberg
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