A
chess clock is actually comprised of two seperate
clocks with a button or switch on each side. They are either
digital or
analog.
After you make your move, you press the button on your side of the clock. This stops the clock on your side and starts the one on the opposite side. Your
opponent is now free to mull over his move while his clock
ticks..
The digital ones are quite
costly, and can run for about $100. The analog ones can be found for about $40-$60.
See Also:
Chess - Time Controls