In each position, if the cube were in the centre, Black would have a perfectly correct initial double. This is because Black is the favourite and he doubles his equity by turning the cube. With Black owning the cube, the situation is different. In the cases where Black does not throw one of his immediate 19 winning numbers, White will have a very powerful redouble. In the diagram position, say Black rolls 41 and plays 5-off. He would have to drop a redouble as White has 29 winning numbers. But if he has not redoubled the original position, then he will still win in those cases where White rolls one of his seven losing numbers. By redoubling, Black reduces his equity from 0.48 to 0.22, a considerable difference.
The paradox is that if White had a stronger position, for example two men on the 24-point, then Black would have a clear redouble! This is because his next roll would then be the last of the game, and White would get no benefit from owning the cube. In this pioneering piece of analysis, Jacoby was one of the first players to demonstrate clearly the power of cube ownership. Even this close to the end of a game, the difference in equity generated by the right doubling decision is huge. It gives one just some idea of the complexity of doubling cube theory.Reuse content