A device used in the game of backgammon
to lever a positional
advantage into a win
. Said to have been invented in New York
in the 1920
's, the doubling cube is a single six-sided die
printed with the powers of two
: 2, 4, 8, 16, 32, 64
. Its function is simply to double the value of the stake
s of the game. Generally used only when playing for money
, the cube is a wonderfully
American contribution to the oldest game
in the world.
At the beginning of the game, the cube is placed midway between the players with 64 up, denoting 1. If at some point either player feels he has a significant lead, he or she may "double", by turning the cube over to 2 and offering it to the other player. Before play continues, the player being offered the cube must decide whether to continue the game at doubled stakes, or forfeit. If he accepts, he takes the cube to his side of the board, and the offering player rolls the dice and play continues. If the double is refused, the refusing player loses the game immediately, with the stakes where they were before the double.
The cube doubles the value of the game each time it is offered and accepted. If I offer and you accept, then later offer it back and I accept, when you finally win, you will have won four games.
The cube multiplies the game stake regardless of gammons or backgammons that may occur, so if you gammon me with the cube as above, you will have won eight games.
The cube can directly show multiples up to 64, but higher stakes are possible; 2 by agreement then means 128 etc. In practice the cube rarely advances beyond 8.
The cube can only be offered at the start of one's turn. If you forget and roll your dice, tough luck; you'll have to wait (and maybe get a disastrous roll and lose your opportunity.)
If a player accepts the doubled cube, they own it; it comes to their side of the board and only they can redouble and offer it again.
House rules often permit the player who is offered the cube, if they think the other player is sadly mistaken to have doubled, to accept and immediately redouble the cube and keep it, before the offering player rolls the dice. This is known as a beaver. In this case the player who offered first usually does not have the option to refuse the beaver and forfeit.
In some places it's also customary to automatically double the cube to 2 if both player roll the same number when determining who plays first, just to spice things up.
When playing for game stakes, a simple win is worth 1 point, a gammon 2 and a backgammon 3. When playing for points, however, the cube multiplies the loser's remaining pieces, so a simple win is worth however many pieces are left when the winner bears off, a gammon is worth 30 points and a backgammon 45. Playing for a dime a point, a single intense game can be worth $24 if it ends up a gammon with the cube at 8!
To speed up extended play, the Jacoby Rule may be invoked to set the value of gammons and backgammons at 1 instead of the usual 2 or 3, iff the cube was never doubled. This discourages players from not doubling (and being refused, thus ending the game) in hopes of winning gammons or backgammons.
The cube is to be treated with respect. Not only is it capable of geometrically affecting your gain or loss, but when you use it you lose control of it. If the game turns sore against you, you could conceivably be forced to refuse the cube and lose a quadruple game only a few rolls after you first doubled. Nor can the cube be safely ignored. Some players simply accept all doubles thrown at them, thereby playing out the "natural" course of each game. Careful timing of your doubles will demonstrate exactly how expensive this "strategy" can be.
The cube is brutally effective at actualizing potential. If you get ahead and throw the cube, your opponent is forced to consider not what lucky rolls they might still get to turn the tide, but what their position is now. It becomes (not so simple) arithmetic: will they lose less by playing out the game, or by forfeit? Players who are unable to distinguish between hope and probability lose all their money.
You should consider doubling the cube if you have a two-roll lead or better over your opponent. However, positional factors are vitally important. If you have a subtantially more solid inner board than your opponent, and are likely to hit them soon, your numeric lead need not be two full rolls; you'll pick up the lead as they fail to reenter your inner board.
Even if you are not numerically far enough ahead to justify doubling, you can use the cube to win against a psychologically demoralized opponent by offering it as they repeatedly fail to bear back in after being hit. This is a major reason I like priming games.
For more delicious backgammon evil, see Backgammon for Blood by Bruce Becker, ISBN 0-380-00384-8. Considered dangerous for beginners because of his deep reliance on back games, it's nevertheless an excellent introduction to advanced play. For completeness I should mention the bible of backgammon, Paul Magriel's Backgammon, ISBN 0-812-90615-2.