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32S-11P-61U-62 vs 32S-11P-61U-63

Posted By: Nack Ballard
Date: Saturday, 8 February 2014, at 7:52 a.m.

In Response To: 32S-11P-61U-62 -- correction (Igor)





White is Player 2

score: 0
pip: 159
Unlimited Game
Jacoby Beaver
pip: 167
score: 0

Blue is Player 1
XGID=-a----EaC---dEa--c-e----B-:0:0:-1:00:0:0:3:0:10

62S-62 [X D10], or 62S-63 [X D48]



There are two aspects to discuss. The first is the relative gain of D vs X when the 4pt is made. The second is the relative gain of D vs X when there is a 2 (or 4) involved rather than a 3.

First aspect: The two checkers that have made the 4pt are no longer used to hit or make other points (except in the occasional case of shifting the 4pt to a lower point). In that sense, the number of active checkers in the zone has been reduced from eight to six. To compensate, there is an increased incentive to supplement the offense by bringing a checker down (in this case with the 2 or 3). I believe this is the main reason that D relatively gains by .039, .036, .049 and .041 in the four nacbracs comparisons of checker play decisions when one owns the 4pt (below) versus those when one does not own the 4pt (above).

Second aspect: For similar reasons that it is more efficient to split against a 10pt builder (I wrote a post on this a few years ago -- the link eludes me at the moment), it is less efficient for the offense to create a 10pt builder. The next paragraph is not meant to be a complete explanation, but I find it easy to remember.

On the follow-up rolls, if Blue has an 11pt builder (or 9pt builder), he will be covering the 11pt/9pt/7pt or covering/hitting back on the 7pt with a diversified number (a 2 or 4). By contrast, if Blue has a 10pt builder, he will be covering the 10pt/7pt or hitting back on the 7pt with a duplicated number (a 3 either way).

David's reason -- that splitting to the 21pt (vs 22pt) tries for a more advanced anchor, is also astute and valid. Moreover, 24/21 has the slight benefit of duplicating 2s (13/11 and 6/4*), though it's a second or third order effect (this factor being more directly relevant for a play like 21S-53S).

Each single diagram (above and below this text) can be regarded as a position "pair," with the roll of 62 and 63 both considered. Using XG++ evaluations, the three "pairs" can be summarized as follows, each case with the 3 (compared to the 2) enhancing X (vs D) by about .04:

--------------------------------------------------------------------------------------------------------

................62S-62 [X D10] "&e...... 62S-63 [X D48] "&e -- swing of .038

........42P-62S-62 [D X29] "&e...... 42P-62S-63 [X D12] "&e -- swing of .041 (+4pt with 42)

32S-11P-61U-62 [D X39] "&e...... 32S-11P-61U-63 [X D7] "&e -- swing of .046 (+4pt with 6/4(2))

---------------------------------------------------------------------------------------------------------

[The second "pair" (below, left) can be alternatively reached by 32S-42P-61U-62 and -63. Looked at another way, the third "pair" (below, right) is identical to the second pair if opening 42 is played illegally as 6/4(2).]

Nack





White is Player 2

score: 0
pip: 159
Unlimited Game
Jacoby Beaver
pip: 161
score: 0

Blue is Player 1
XGID=-a--B-DaB---dEa--c-e----B-:0:0:-1:00:0:0:3:0:10

42P-62S-62 [D X29], or 42P-62S-63 [X D12]
White is Player 2

score: 0
pip: 159
Unlimited Game
Jacoby Beaver
pip: 163
score: 0

Blue is Player 1
XGID=-a--B-CaC---dEa--c-e----B-:0:0:-1:00:0:0:3:0:10

32S-11P-61U-62 [D X39], or 32S-11P-61U-63 [X D7]



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