Most dive watch style bezels have a ring of numbers around them that increase as you go around. They often have smaller increments in the beginning, to give finer control, but generally move around in 5 minute increments.
On of the classics of the genre is the Submariner from Rolex shown below. The bezel rotates and locks into position allowing you to see how much time has elapsed.
The countdown bezel operates in the reverse, showing you how much time is remaining instead. You can see an example below from Standard Issue Instruments (The Pilot Mission Timer). The numbers start at 60 at the top (shown with the arrow) and then count down in single increments with every 5 minutes shown in numerals. This is a typical layout of a countdown bezel.