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Position of the Day 02-18-26

Posted By: Chuck Bower
Date: Friday, 20 February 2026, at 8:10 p.m.

In Response To: Position of the Day 02-18-26 (Stick)

Consider the following (reference?) position from Robertie's Advanced Backgammon, 2nd ed. vol. 1, position 144, page 198:





White is Player 2

score: 0
pip: 83
Unlimited Game
Jacoby
pip: 108
score: 0

Blue is Player 1
XGID=aBBBBBB-----------AccccbB-:1:1:1:00:0:0:1:0:10
Blue on roll, cube action?

Analyzed in Rollout No redouble Redouble/Take
Player Winning Chances: 62.89% (G:2.08% B:0.02%) 62.37% (G:1.56% B:0.02%)
Opponent Winning Chances: 37.11% (G:6.15% B:0.20%) 37.63% (G:6.11% B:0.17%)
Cubeless Equities +0.215 +0.401
Cubeful Equities
No redouble:+0.407±0.001 (+0.406..+0.409)
Redouble/Take:+0.186 (-0.221)±0.002 (+0.184..+0.188)
Redouble/Pass:+1.000 (+0.593)
Best Cube action: No redouble / Take
Percentage of wrong pass needed to make the double decision right: 21.4%
Rollout details
10368 Games rolled with Variance Reduction.
Dice Seed: 29834315
Moves: 3-ply, cube decisions: XG Roller
Double Decision confidence:100.0%
Take Decision confidence:100.0%
Duration: 2 minutes 52 seconds

eXtreme Gammon Version: 2.10

Here there are few gammon wins for Blue. In the problem position, let's assume 1/3 of Blue's wins and 1/6 of White's wins will be gammons. Further, let's assume that the cubeless equity at the drop/take point is 0.55. Finally we'll ignore backgammons. Let 'W' represent Blue's winning chances at the drop/take point. Then:

W + W/3 - (7/6)*(1 - W) > 0.55.

Solving for W gives the Drop/Take point at 69% wins for Blue. Comparing to the reference position, can Blue win an extra ~6.5% games? Note Blue has about 6 more pips of timing in the problem position (non-trivial plus) and that most of the time White will have two checkers on the bar if/when Blue's board starts to go South. White's homeboard spares aren't as nicely placed in the problem position, and if Blue can prime White's (eventual) 24-pt anchor Blue may have time to force White to crunch. Do all those add up to 6.5% more wins? Probably close but I'm going to say 'yes'.

R+P.

P.S. For ~30 years since I read this book I've remembered a quote which happens to accompany Robertie's analysis of this reference position: In prime vsersus prime positions, it is often correct to redouble your opponent out of the game, rather than redouble him in. I wonder if in the bot era he still feels that way. FWIW, IMO this book was the best backgammon book written in the pre-bot era, which was in its death throes when Advanced BG first published (1991). TD-Gammon was already in the works and Jellyfish's release ~4 years away.

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