Analog or digital chess clocks and their purpose.
The game clock or in this case chess clock, features two adjacent clocks with stop and start buttons, when one clock is stopper the other is started, so they are not running at the same time.
The purpose is to keep the game moving, keeping track of each player’s total time taken before they move their game piece.
In the opening moves the pace can be very rapid and slowly down as the game progresses and each opponent’s strategy comes into play.
There are variations of time that can be used such as a sudden death scenario where several moves are made in a prescribed time or the game is forfeited.
There is also a version where the entire game is played in a predetermined time frame.
The United States Chess Federation preference for the clocks:
The most preferred are units that offer a time delay feature.
Mechanical clocks are preferred over digital clocks.