minutes per side with a 10-point penalty for each minute or part thereof that is used in excess, so that overstepping the allotted time by 61 seconds carries a 20-point penalty. Hourglass Each player's clock starts with a specified time (such as one minute or ten minutes). While one player is deciding a move, their clock time decreases and their opponent's clock time increases. This is analogous to an hourglass: sand empties from one container and fills the other. The sum of both clocks always remains the same, and slow moves give extra time to the opponent. There is no maximum amount of time allotted for a game with this timing method; if both players play quickly enough, the game will continue until its natural end. Use of this time control is uncommon. Game formats Go Byo-yomi This timing method is also used in shogi. The word is borrowed from Japanese; the term literally means "counting the seconds", or more generally, "countdown". After the main time is depleted, a player has a certain number of periods (for example five periods, each of thirty seconds). If a move is completed before the time expires, the time period resets and restarts the next turn. If a move is not completed within a time period, the time period will expire, and the next time period begins. This is written as + of . Using up the last period means that the player has lost on time. In some systems, such as certain Go title matches, there is no main time; instead, the time used is rounded up to the nearest whole increment, such as one minute, and the actual counting of time occurs toward the end of one player's time. A typical time control is "60 minutes + 30 seconds byo-yomi", which means that each player may make as many or as few moves as they choose during their first 60 minutes of thinking time, but after the hour is exhausted, they must make each move in thirty seconds or less. To enforce byo-yomi, a third person or a game clock with a byo-yomi option is necessary. In professional Go games and many amateur tournaments, a player has several byo-yomi periods, for example five periods of one minute each. If a player makes their move within a one-minute period, they retain all five periods for their future moves. If a player oversteps one