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LAST WEEK we began to look at "Efficient Doubling". An efficient double is one where the doubler gets the maximum benefit in equity at a given time from doubling his opponent. To look at an example, let's first look at an inefficient double.

In the position above, black should not double - if he does so, white has a correct beaver. Now let's suppose that black rolls 61 and plays 22/16, 12/11 (he could play 6/5 with the 1 but that is weaker than leaving the point slotted). If white now fans, black has a double that is so strong that white must pass. In two rolls, black has gone from not being good enough to double to losing his market. Pleased as he will be to win the game, he has not made optimal use of the cube. What he would have liked is to give white a very difficult decision. Here, all of white's decisions have been easy.

Prime vs prime positions such as this tend to lead to inefficient doubles. In contrast, blitz positions often lead to efficient doubling situations. For example, white starts the game 64, played 24/14 and black responds with 55, played 8/3(2), 6/1(2)*. If white now fans, black has an "efficient double" - one that potentially maximises his equity.

Knowing what type of positions lead to what type of doubling situations is increasingly important. Experts steer for particular game types to maximise their use of the doubling cube.