Forum Archive : Strategy--Backgames

Which anchors are best?

From:   Chuck Bower
Date:   21 January 1997
Subject:   Re: How bad is this hit?
Google:   5c34a9$

Dan Scoones wrote:
> Last night on FIBS I played my first-ever match with TD_one.  After
> splitting my back men and getting pounded by a quick 55, I managed to
> struggle my way to this 2-5 backgame:
> +-24-23-22-21-20-19-+---+-18-17-16-15-14-13-+
> |  O  X  O  O  X  O |   |     O             |
> |  O  X  O  O  X  O |   |     O             |
> |        O  O  X  O |   |     O             |
> |                   |   |                   |
> |                   |   |                   |
> |                   |   |                   |
> |                   |   |                   |  [1]
> |                   |   |                   |
> |                   |   |                   |
> |                   |   |                   |
> |           X       |   |                   |
> |        X  X     X |   |     X             |
> |        X  X  X  X |   |     X          O  |
> +--1--2--3--4--5--6-+---+--7--8--9-10-11-12-+
> 1-point match
> O: TD_one
> X: rook
> X to play 65
>  (snip)
> I played 20/9..., and managed to cover my 5-point just before TD_one
> was forced to break into a double shot.  I hit the shot and went on to
> win a close race.

    I realize that Kit answered this question already, but here are
    some "quantitative" results.  I ran JF level-6 cubeless (money play)
    rollouts and it gave the following results:

    play       X's % winning chances (std. dev.)     money cubeless equity

    20/9                33.6(1.4)                       -0.548(0.038)
    20/15,8/2           29.3(1.8)                       -0.730(0.050)
    20/14,8/3           27.9(1.3)                       -0.729(0.034)
    23/12*              28.5(1.6)                       -0.850(0.048)

    Thus JF agrees with your play, both for money and at DMP.  (Note
    that JF is really playing with gammons ("money play") so the
    percentage wins will probably be differenent at DMP.  Still, we
    can probably accept the RELATIVE values (winning chances) of these

>  (snip)
> ...what is the probability that a properly-timed
> 2-5 backgame will yield a direct shot?  I've heard pretty convincing
> evidence that it's one of the weakest two-point backgames of all.

    I can't answer this question, but I find your last comment surprising.
Robertie's "Advanced Backgammon" doesn't agree with this "2-5... is one
of the weakest two-point backgames of all."  (WARNING:  I am speaking
from memory, since I don't have his book in front of me.)  BTW, here I
am assuming that by "two-point backgames" you mean "games where backgamer
has exactly two of his/her opponent's inner board points".  One way to
divide these up is to look at the number of points between the two you
actually hold:

No points between:     12, 23, 34, 45

One point between:     13, 24, 35

Two points between:    14, 25

Three points between:  15

(I realize that backgames with the opponent's 6-point do occur, but they
are so rare that I don't feel the least bit confident to even comment.)
My distorted view of recent backgammon history (1970 to present) recalls
that originally the 12 and 13 were the backgames that were talked about.
Players quickly found that the 12 is EXTREMELY difficult to time.  Then
the 13 and 23 were considered the best.

     As time progressed, there arose a feeling (maybe just mine;
history has a way of getting fuzzy) that IN GENERAL the value of a
two-point backgame decreased with the number of points between.  (NOTE
that I said "IN GENERAL".)

     In "Advanced Backgammon", I seem to recall that Robertie calls the
2-5 backgame quite playable, which surprised me when I first read it.
Since then my limited experience with the 2-5 has been positive (probably
not "positive equity", unfortunately).

     As far as I know, no one has performed a systematic study of the
relative merits of the different backgames using the new robots.  Does
anyone out there want to take on this task??  You may go down in history
as the first person to really understand the relative strengths and
weaknesses of the different two-point backgames!  (Or maybe not...)

      c_ray on FIBS
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After an early blitz attempt  (Daniel Murphy, Apr 1997) 
But they're so much fun!  (Laury Chizlett+, Oct 2000) 
Checker problem  (David Montgomery+, May 1995) 
Defending against a backgame  (KL Gerber+, Jan 2003)  [Long message]
Defending against a backgame  (Michael J. Zehr, Jan 1995) 
How many men back?  (Brian Sheppard, July 1997) 
Play for a backgame from the start?  (Alan Webb+, Dec 1998) 
What is a backgame?  (Daniel Murphy, Apr 2001) 
When to double  (David Montgomery, May 1995) 
Which anchor is best?  (Kit Woolsey, July 1996) 
Which anchor to break  (Brian Sheppard, May 1997) 
Which anchors are best?  (sebalotek+, Jan 2012) 
Which anchors are best?  (Adam Stocks, Apr 2002) 
Which anchors are best?  (Mary Hickey, Mar 2001) 
Which anchors are best?  (Jerry Weaver+, Apr 1998) 
Which anchors are best?  (Chuck Bower, Jan 1997) 
Which anchors are best?  (Marc Gray, Nov 1995) 

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