<P> The exact approach to using a game clock to regulate games varies considerably . </P> <P> This is the simplest methodology . Each player is assigned a fixed amount of time for the whole game: once a player's main time expires, he loses the game . </P> <P> Each player's clock starts with a specified time (e.g. 1 minute, 10 min etc .). While Player 1 is deciding a move, player 1's clock time is decreasing and Player 2's clock time is increasing . This is similar to how an hourglass works; sand empties from one container and fills into the other . Moving slowly gives your opponent extra time . The sum of both clocks will always remain the same . There is no maximum amount of time allotted for a game with this timing method; as long as both players play quickly, the game will continue until its natural end . When time runs out on one player's clock the game is over and that player loses . Use of this time control is uncommon . </P> <P> Here the game time is separated into two basic domains: the main time, and the overtime . To switch between the two requires some trigger event . Often this is the expiration of the main time . In chess, reaching a fixed number of moves can trigger the gain of a fixed amount of bonus time . This is the general chess rule and it usually occurs in long games after the 40th move: e.g. 120 minutes to complete the first 40 moves, and another 30 minutes to complete the entire game . </P>

How many minutes in eight 30 second periods