A typical chess clock.

A game clock consists of two adjacent clocks and buttons to stop one clock while starting the other, such that the two component clocks never run simultaneously. Game clocks are used in two-player games where the players move in turn. The purpose is to keep track of the total time each player takes for his or her own moves, and ensure that neither player overly delays the game. Photo of chess clock by LDC, released to the public domain. ... Photo of chess clock by LDC, released to the public domain. ... A clock (from the Latin cloca, bell) is an instrument for measuring time. ... A game is a recreational activity involving one or more players. ...

Game clocks were first used extensively in tournament chess, and are often referred to as "chess clocks," but their use has since been adopted for tournament Scrabble, Shogi, Go, and nearly every competitive two-player board game. Many countries claim to have invented the chess game in some incipient form. ... Scrabble board in play. ... Shogi (将棋 shōgi) is one of a family of strategic board games, of which chess and xiangqi are also members, which originated from the 6th century Indian game of chaturanga or a close relative thereof. ... Go is a strategic, two-player board game originating in ancient China between 2000 BC and 200 BC. Go is a popular game in East Asia. ... A board game is any game played with a premarked surface, with counters or pieces that are moved across the board. ...

The simplest time control is "sudden death", in which players must make a predetermined number of moves in a certain amount of time or forfeit immediately. A particularly popular variant in informal play is blitz chess, in which each player is given five minutes on the clock for the entire game. A time control is imposed on the tournament play of almost all two-player board games to ensure that neither player delays the game or gains an unfair advantage by thinking for an unduly long time. ... Blitz chess (also known as speed chess or blitzkrieg chess) is a game of chess where each side is given very little time to make all of their moves. ...

The players may take more or less time over any individual move. The opening moves in chess are often played quickly due to their familiarity, which leaves the players more time to consider more complex and unfamiliar positions later. It is not rare in slow chess games for a player to leave the table, but the clock of the absent player continues to run if it is his turn, and/or starts to run if his opponent makes a move.

Analog clocks (as pictured above right) are equipped with a "flag" (a Dutch invention) that falls to indicate the exact moment the player's time has expired. Unfortunately, additional time can't easily be added for more complex time controls, especially those which call for an increment or delay on every move, such as some forms of byoyomi. Therefore more versatile digital clocks are becoming increasingly popular. Byo-yomi is an extended time control in two-player games, specifically Shogi and Go. ... A digital system is one that mayoperate on digital signals, i. ...

Digital clocks and Internet gaming have spurred a wave of experimentation with more varied and complex time controls than the traditional standards. One particularly notable development, which has gained quite wide acceptance in chess, was proposed by former world champion Bobby Fischer, who in 1988 filed for U.S. Patent #4,884,255 (awarded in 1989) for a new type of digital chess clock. Fischer's digital clock gave each player a fixed period of time at the start of the game and then added a small amount after each move. In this way, the players would never be desperately short of time, but games could also be completed more quickly, doing away with the need for adjournments (in which a game is left incomplete to be finished at a later date). Although it was slow to catch on, as of 2004 a very large number of top class tournaments use Fischer's system, though usually in combination with the more traditional (at lower levels, more traditional clocks are still employed as they are cheaper). Other aspects of Fischer's patent, such as a synthesized voice announcing how much time the players have, thus eliminating the need for them to keep looking at the clock, have not been adopted. Bobby Fischer. ... The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ...

External links

• US Patent No. 4,884,255 for Fischer's clock