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Chess Clocks
'Is it my move? I thought it was your move!'

A common image of chess players is two people hunched over a board fully concentrated on what seems to be nothing happening. They think and think. Finally one of them reaches out and moves a piece. Then they fall back to silent concentration.

Another image is the same two players moving pieces rapidly in turn, taking no time for reflection. One player moves and slaps a clock at the side of the board; the other moves immediately, almost instantaneously, and slaps the same clock. The players continue rapidly moving and slapping until one of them suddenly stops the clock.

The difference between these two scenarios is the presence of the clock, controlling the time available for thought during a game. The clock tracks the time each player uses, adding a dimension to the game which moves it closer to the world of sport.

Purpose of a clock

A chess clock has two connected time displays, linked in such a way that only one clock can run. When one of the clocks is stopped the other starts.

The clock runs for the player who is on the move. A player makes a move then stops the running clock, automatically starting the opponent's clock. Unless the move has ended the game, the move is not completed until the clock has been stopped.

A chess clock can be used to control access to any scarce shared resource. Two children can peaceably share a computer with the help of a chess clock.

The application to chess is that all moves must be made within a given time limit. A player who has not made the required number of moves loses the game on time.

History of clocks

The idea for chess clocks took root in the mid-19th century. Thomas Bright Wilson (1843-1915) of Manchester, England, is generally credited with the invention of the first chess clock, used for the great London international tournament of 1883. The first patent for a clock was issued in 1884 to Amandus Schierwater of Liverpool.

Modern analog clock

The flag, located a few minutes left of 12:00, signals the exact instant when a player's time expires. Flags were first proposed in 1899 by H.D.B. Meijer of the Netherlands. In the early days of clocks, overstepping the time limit was not equivalent to losing a game. Claiming a win was considered unsporting.

Digital clock

Digital clocks were introduced in the 1980s. These allowed more sophisticated time controls than are possible with an analog clock.

The Fischer clock gives a player a fixed time plus additional time after each move. This avoids the worst time scrambles, where a player may have a few minutes to make 10-15 complicated moves.

The time delay clock gives both players a main thinking time plus a fixed time for every move. The countdown of the main time starts only after the fixed time has been used. If a player moves before the expiration of the fixed time, the main time does not change, even if the fixed time has not been used completely.

A player who does not complete the required number of moves in the allotted time does not always lose the game. If the position on the board is such that the opponent cannot force checkmate by any sequence of moves, the game is drawn because of insufficient material. Also, if both flags fall and it is impossible to establish which flag fell first, the game continues. Each player is responsible for pointing out that the opponent has lost on time.

How a clock is used

In a friendly game, Black chooses the side of the board on which the clock is placed. Right-handed players usually prefer the clock on the right; left-handed players prefer the left. In a tournament game, the arbiter decides where the clock is placed.

The game starts when White's clock is started. On an analog clock, the flag is usually set to fall at 6:00. That means for a 30 minute time control the clocks are set at 5:30, while for a 2 hour control, the clocks are set at 4:00. Both players often receive a few extra seconds to compensate for any small imperfections in the clock or the flag.

The rules require that both players handle the clock properly. Players must use the same hand to move the piece and press the clock. They can't keep a finger on the clock or 'hover over it'. It is also forbidden to punch it forcibly, pick it up, or knock it over. The penalty can be loss of the game.

The time limit for a game is also known as the time control. The earliest time controls were for a fixed time per move, but it was soon recognized that this was not optimal. Much more common is a fixed time for a certain number of moves or for an entire game. This allows easier tournament planning and scheduling.

Serious tournament games often have an initial time control of 40 moves in 2 hours, followed by a second control of 20 moves in 1 hour if the game continues beyond 40 moves. After this, a sudden death finish of a half-hour per player decides the game. Games with intermediate controls of x moves in such-and-such a time require that both players write down the moves to know when they have reached the time control. Claims following time trouble in tournament games are regulated by special rules on the obligations of the players.

Blitz games have time limits of 5 minutes per player for the entire game. Rapidplay games have time limits of 30 minutes per player per game, also known as game/30.

It's not necessary that both players start a game with the same amount of time. Different amounts of time -- like 5 minutes vs. 1 minute in a blitz game -- can be a good equalizer between players of unequal strength.

The most important thing to remember about a chess clock is that you must press your clock after you have moved. Your opponent has no obligation to inform you when you forget to do this.

Even World Champions can forget. During the second game of the 1987 Kasparov - Karpov title match ('KK IV'), in a difficult position with a few minutes left on his clock, Kasparov forgot to stop it after playing his 26th move. When he finally noticed, he had only one minute left. He resigned on his 33rd move.


Photos in this article are reprinted with permission of ChessExpress.com.

 Related Resources (offsite)
• Digital chess clocks
• Analog chess clocks