The 4 cube is the bg equivalent of the Mighty Hammer of Thor, deadly in the right hands. The player prepared to ship a 4 cube at the first opportunity will wreak havoc at all levels below World Class. The possesion of the cube can be worth a lot, but only if you are prepared to use it! In a recent match I had two opportunities to use it. Here's the first.
You are Black, holding the 2 cube in the first game of a 9 point match. What's the correct cube action for both sides here?
The first question to ask yourself, always, is "If I was White, am I 100% certain that this is a take? If not, it must be a double." This is known as Woolsey's Rule. Pretty clearly you can't be certain that this is a take, with two men on the roof against a four point board, so Black is good enough to redouble. Now move on to question two. "Am I 100% certain that this is too good to double? If yes, play on for the gammon for at least one roll, if no, turn the cube." This is known as dorbel's rule. Purists don't like this rule, but in practical terms it performs quite well.
So, what's the answer? This is a correct redouble and a correct pass, even though Black's checkers are not well placed to close the board and he still has one checker behind a five prime. Failing to cube or taking the cube are both small blunders costing about 1/10th of a point.
Dorbel's rule works quite well in situations where the decision to cube or play on isn't clear, because if you get a pass it puts two concrete points onto the scoresheet and when you get a take in this position , as you often will, you gain 2/10ths of a point in theoretical equity. Actually you often get takes in positions much stronger than this and passes in positions that are much weaker. The point of cubing, often missed, is that it allows your opponent the opportunity to make a mistake. The Mighty Hammer of Four is a terrifying weapon.
The big temptation is to play on in the hope that if things go well you will win a gammon and if things deteriorate, you'll be able to cash later. That's often the case of course, but it's easy to see here that an "ordinary" number for Black, 5-3 say, followed by the same number for White will leave Black in a position where not only can't he cash, but he won't even have a redouble!
I failed to redouble that one, forgetting my own rule! TIP:More mistakes are made by forgetting the things that you already know than are made from technical ignorance.
Later on I led 4-2 to 9 and holding the cube, got down to this juicy position.
Thorp Count . This old fashioned formula is very easy to apply and if you make some little adjustments for gaps, can be very accurate.
Actually here, Thorp rates this as an initial double but not a redouble and given that Black leads in the match he should be a little more conservative than usual in bringing a large cube into play. Nevertheless, making a small adjustment for White's gap makes a difference. Also, Black will get some incorrect passes here and with the end of the match so close, White's opportunities to redouble to 8 are going to be limited, so I finally turned it and White correctly took. Both actions are correct.
Note that Woolsey's Rule still works here. I couldn't be certain that this is a take for White, fairly confident yes, 100% certain, no. If the cube dies with this turn, at 0-0 to 3 say, this position is a marginal take/pass, so a useful reference position.
When you take a 2 cube, part of your equity lies in your willingness to use it if things go your way. Don't be afraid to use it! Swing that Mighty Hammer and reap the rewards.