FIBS Board backgammon forum

I'm not smart enough to figure this out on my own, so I'm asking for help here.

In the attached position, the score is 0-0 in a 7 point match. White doubles.  (position/match ID: bDtIwGBzZwYIMA - AhngAAAAAAAA)

According to gnubg, by passing you lose around 12% MWC. Why?  Black has two men on the bar and two blots in the outfield. I would think that it wouldn't be too much trouble for white to keep him busy on the bar until he escapes the back men.

What am I missing?

You've not made it clear here but it's implied from the picture that this is a rerecube to 8 and thus an offer to play for the match. Black will be in this match to the end should they take as they have no timing problem and, crucially, have anchored on whites golden point. It's not a major "cost" if white picks up more blots as this only improves black's timing. Also important is the constraining of white's 5s and 4s where they'll be forced to advance or give up the 8 point.
The "duplication"(ish) of one of white's 6's (eg white rolls 61 and makes their 2 point) is also useful as it removes one of the running chances from the two pieces on 24.
A good way to think of this (that is IF its a rerecube to eight) is that white is likely to win with a gammon anyway and thus is getting poor value from their double.
All of that was done without the aid of GnuBG --- I hope I'd recognise how good a take it was if I were black!


Steve

Two important things here:

1) Score. If black passes he will give big lead to white. According to gnu match equity table, black would have only 23,486 % chances to win the match. So black will need more then those chances to win this game and the match to justify the take.

2) The prime. Big wisdow from gnu (and other programs) is that even a small prime can be major trouble (if there is more then one checker behind it). What can happen here? White has only couple of pieces to move here and two pieces behind prime. Not much time to roll the sixes. If white rolls doubles (not 66 or 11) he is very likely to crash his home board immediatly. The same happens if white doesn't roll six (or one and five) in couple of turns. Or he might escape and then the other checker might get trapped with unlucky doubles. And also black has very strong home board. So if black get his checkers out from the bar and gets lucky hit he is likely to win the match. Or black might get his lucky shot even later when white is bearing off. The blots and the checkers on bar doesn't matter much here because gammons doesn't count (if they would this most certainly would be pass). All these chances add up much more then 23,5 %.