Chess clock

A chess clock has two connected time displays arranged so that only one runs at a time. Each player uses time on their own display while thinking and making a move.

After moving, the player presses their side of the clock. This stops their own time and starts the opponent's. The interval between releasing the piece and pressing the clock still belongs to the player who just moved. Under the over-the-board rules of the International Chess Federation, the clock must be pressed with the same hand used to move the piece.

Common ways to allocate time

• Fixed time: each player receives a reserve that decreases while that display is running.
• Increment: before each move, a specified amount is added to the player's available time.
• Delay: a short grace period passes before the main time begins to decrease.

Flag-fall is the physical or digital indication that a player's allotted time has expired. Failing to complete the required moves in time normally loses the game. The result is a draw, however, if the opponent could not checkmate through any legal sequence, a situation related to insufficient material.