Potential for Atomic Clock Wristwatches

The complete working clock would be sugar cube-sized and would run on just 73 milliwatts -- small enough for it to be incorporated into battery-powered handheld devices such as mobile phones.
The clocks currently used in most electronic devices are based on quartz oscillators, in which minute vibrating quartz crystals produce precise pulses. But their accuracy can be adversely affected by factors such as temperature.
By contrast, the atomic clock would be accurate to within a second every 300 years, making it more than 1,000 times more reliable than a very good wristwatch.