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Confused by large equity difference

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08-19-2018 , 06:05 AM

Soulwaxical

adept

Join Date: Sep 2011 Posts: 1,021

Hi guys, getting back into backgammon and just has this situation come up. Im REALLY rusty so the answer is probably obvious but why does XG think Bar24 13/9 is +0.119 better than Bar24 14/10?

All help appreciated

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08-19-2018 , 01:34 PM

Robertie

old hand

Join Date: May 2004 Posts: 1,954

Your diagram shows Black on the bar, but the game score shows White on roll and coming in from the bar. There's some sort of mixup here.

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08-19-2018 , 01:52 PM

_Z_

adept

Join Date: Jul 2004 Posts: 720

The diagram shows the position after White makes one of the candidate plays (B/24 13/9). It is confusing.

The equity difference is somewhat magnified by the fact the Black has a cube after either play, but it's more efficient after B/24 14/10.

But you'd rather have a loose checker on the 9 than the 10 because it duplicates both of Black's entering and hitting numbers (5s and 4s).

You might rather have a loose checker on the 13 than the 14 despite the duplication argument for having it on the 14 due to the fact that White will have more return shots when that checker is hit.

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08-21-2018 , 09:24 PM

Robertie

old hand

Join Date: May 2004 Posts: 1,954

13/9 looks correct at first because of the duplication of 5s and 4s, as z said. However, that duplication is an illusion, I think. If we actually count Black's hits from the bar, I get 14 hitting rolls after either play.

Looks to me like the real difference comes when Black either fans or enters without hitting. Now White has 6s to escape and 5s to hit on his 4-point. In effect, with 14/10 White is duplicating his own 6s on the next roll.

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08-28-2018 , 07:07 PM

Rapid_Fire

grinder

Join Date: Jun 2011 Posts: 469

I'm curious if you took off the Jacoby if 13/9 becomes preferable to 14/10.

I instinctively prefer Bar/24, 6/2 but I guess I'm wrong.

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08-31-2018 , 12:07 PM

_Z_

adept

Join Date: Jul 2004 Posts: 720

The Jacoby rule affecting a checker play is rare, especially if the two plays are pretty similar in terms of gammon percentages.

Jacoby will turn some non-doubles into doubles when the position is very gammonish and volatile, but that's about it.

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08-31-2018 , 06:47 PM

Rapid_Fire

grinder

Join Date: Jun 2011 Posts: 469

Quote:

Originally Posted by _Z_

Yes, but if there were no Jacoby, it would seem 14/10 would be worse than 13/9. It is very slight chance, but should white roll presto it will almost cetainly result in a gammon. The Jacoby option is stopping that possibility.

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