All timekeeping machines need something as the reference. Sundial
uses the sun, Mechanical clock uses pendulum, Mechanical watches
use balance wheel, and Quartz watch uses quartz crystal.
For atomic timekeeping, atoms are used. Atomic clocks do not use
radioactivity, but rather the precise microwave signal that electrons
in atoms emit when they change energy levels. Early atomic timekeeping
machines were masers with attached equipment. Currently the most
accurate atomic timekeeping machine is based on absorption spectroscopy
of cold atoms in atomic fountains.
Since 1967, the International System of Units (SI) has defined
the second as the duration of 9,192,631,770 cycles of radiation
corresponding to the transition between two energy levels of the
Comparing with the quartz crytal, 32,768 Hz, Atom gives out a much
higher reference frequency which maintains an accuracy of 10-9
seconds per day or 1 second per 2,739,726 years !!!
I do think you are going to buy an Atomic Watch becuause of its
accuracy; however, you cannot. This is because there is no such
thing at this moment. This is because even the smallest Atomic Clock
is bigger than a desktop PC.
On the market, there are many "Atomic Watches",
they cost as low as US 25, but they are not atomic watches.
These atomic watches are Radio Controlled Watches --- A watch
can automatically adjust the time according to the Radio Signal.
The Most famous and common Radio Controlled Watches are designed
by Casio, it is called Wave Ceptor which the radio-controlled
function of the high-end products
is multi-region, allowing you to switch from UK, USA, Japan,
China and mainland Europe transmitters. The Wave Ceptor range
will also automatically adjust for daylight savings time.
The one on the left only accepts US WWVB, UK MSF Frequency:
US, UK 60kHz signals.
This one is one of the high-end products which accepts UK,
USA, Japan, China and mainland Europe signals.
Price : ~ US $ 400