Nothingness: You should read the rules again. If a player doubles, the other player must accept or concede the current game. If the opponent concedes, then the doubling player immediately wins the current game and receives a number of points equal to the current value of the game before the double. For example, if no player has previously accepted a double in the current game, it is worth 1. After one double is accepted the game is worth 2, after 2 doubles it is worth 4, and so on. If the opponent accepts, then play continues normally at the increased stakes. So it normally makes no sense to double when you are hopelessly behind, because you are just doubling the amount your opponent will win (and giving him the opportunity to redouble). A player who wins an undoubled game wins 1 point, unless the win is a gammon (2 points) or a backgammon (3 points). If the game has been doubled and accepted once, then a single game is worth 2 points, a gammon 4, and a backgammon 6.

Until the cube has been turned (i.e., until a double has been offered and accepted) either player can offer a double before rolling the dice on his turn. Once a double has been accepted, then only the player accepting the double can offer another double. In this way "possession" of the doubling cube passes back and forth between the players, changing hands after each accepted double in the current game.

One other doubling rule is the "Crawford Rule." The Crawford Rule states that, when one player reaches a score that is only one point away from winning the current match, his opponent may not double in the next game. After that game (called the "Crawford game", which BrainKing erroneously calls the "Crawford Round", the trailing player may double normally.

Nothingness: the doubling cube only makes sense in a match of more than 1 point

by declining the cube offer you will lose that game, but not the match (unless if its the last point your opponent needs)

in the end game when you are far behind your opponent, your opponent can offer the double, you will of course decline, and the game will finish a bit faster :)

in the end game when both are not that far apart, one can offer a double if he think he will win .. if he was correct then he wins double the points he would have otherwise won

the trick is to find where you will still win, and your opponent might still accept .. i you can notice that position, then you win double the points your opponent might win in the same kind of game, and you might win the match although your opponent might be of equal strength in backgammon without the cube

of course there is a bit more as alan explained : when the doubling cube is available you can also win gammons and backgammons .. a gammon (no men beared off by your opponent) is worth 2 points, without any doubling applied yet, a backgammon (opponent still has a men in the starting quarter or on the bar) is worth 3 points ... so a game which was doubled once and became a backgammon .. is worth 6 points :)

now the trick is to find out .. when you are winning a game .. wether you can turn it into a gammon (which will give you 2 points without doubling) or if you wont be able to do so .. if you double and your opponent declines you will only get 1 point .. but it is a certain point

the best way to learn it is to try it :)

Hrqls: Good points.

The strategy of using the cube is subtle, despite its apparent simplicity. Like all plays in backgammon, it depends upon the odds of various outcomes. These are easier to illustrate if one assumes a "money" game is being played rather than a match of finite length. In a money game, the winner of each game wins an amount of money equal to the agreed stakes multiplied by the value of the cube. So, for example, if we are playing for $1 a game and you win a doubled gammon, I owe you $4. Each game is self-contained so there is no match winning strategy to consider.

Now, assume we are playing a money game for $1 a game and after several moves I offer you a double. (Assume we are of equal playing ability.) You examine the board situation and conclude that your chances of winning the current game are only 40%. Should you accept the double, or drop it (concede)?

The intuitive answer is to drop, because you are more likely to lose than to win, and accepting doubles the stakes. But surprisingly, the correct action is to take the double. This can be shown mathematically.

If you drop, you will lose $1 immediately. If you accept the double and play on, you have a 60% chance of losing $2 (net value of minus $1.20). However, you also have a 40% chance of winning $2 (net value of plus $0.80). Therefore, the total net value to you of accepting the double is minus $0.40. Since this is better than the minus $1 cost of dropping, you should accept and play on.

Accepting a double actually increases the net value of the game somewhat, because after accepting you are in possession of the cube and only you can make the next double. This turns out to be a very significant advantage in some cases.

alanback: LOL would you accept a IOU if i didn't have any money LOL:)

"Have Fun": I don't play for money on the Internet :-)

alanback: Wise man you are:)))

alanback: great points that you and Hrqls have made on the cube... however as you both know this only skims the surface on the 'theory of the cube'....
...alanback, a few years back you had a link to a very informational 'cube theory' article... I must say I was enlightened on many things by reading it and it explained things in more far more detail than either of you posted here... I don't know if you still have it , or even remember it, but it explained why one should offer the cube, and when to offer it... it also explained the advantages of cube possesion, and why one should accept early in a game...
if you remember this link, or still have it, I think it would be great reading for the enquisitive minds interested in better knowledge of the cube, or simply for someone that wants to better their gammon play and/or experience...

LionsLair: I don't have it at hand, but I will try to dredge it up.

LionsLair: Is this what you were asking about?

http://www.geocities.com/alanback/deja/BGthoughts.htm#Gammons

alanback: yes, that looks very familiar... I seem to remember this and other theories on the cube when I started fine tuning my gammon skills, with better knowledge of the cube (when to offer/accept/decline)
... for anyone that wants to better their play and/or knowldge on the subject,this is great reading...(understanding simple mathmatics helps too!)
...thanx for dredging that up!

Nothingness: like this position. i might be able to finish the game before he gets all his men home and bears 1 off ... that would give me 2 points (3-0 in the 7 point match) ... but .. i think i wont be able to gammon him .. i think the wisest action for me would be to offer the double .. so that he would decline .. giving me 1 point (2-0 in the 7 point match) .. by offering the double and getting the game i wont risk being caught by his single piece in case i roll badly and leaving a single men
but as i am not a wise man .. and i like to gammon .. i wont offer the double yet and just risk a bit for this 1 extra point (gammon) and hope i wont roll something like 6+3 twice in a row

Hrqls: In this precise example I think that your analysis is missing an important concept, the one of "market losers". But I don't want to comment too much on an ongoing game, and anyway I will try to put some cubing concepts together in an article for brainrook.com :-)

nabla: ah yes please ... that would be great! .. i only learned about the cube when it came online on here and know very little about it .. just what i just mentioned :)

1 thing which i didnt mention is that my opponent probably doesnt want to leave his spot there because its his only chance to send me back .. therefore he will probably move his other men first and giving me more opportunities for a gammon (unless he rolls a 6 ;))

we are a few moves further now and i decided to open up a bit in favor of bearing off extra men .. it leaves me more vulnerable though .. but i think i need that if i want to gammon him :)

please dont give hints or strategies which can be used in this game while its going on though ..

i am explaining my own thoughts in this one .. which might help my opponent .. but thats my own choice ;)

btw nable and i have a game going as well with a nice doubling example .. if i remember correctly from about half an hour ago :)

Hrqls: Now I re-read my message and it really reads too much mysterious, sorry, I'd better said nothing. But after the game is finished I would with pleasure discuss the position with you in a clearer way !
Yes, nice example we had, I thought that at the beginning you were wrong not to double, but it surely turned very much in your favour as it is now a very probable gammon.