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January 6, 2012

Gammon Go

Continuing to look at match play basics.  This time we look at Gammon Go.

Kit Wolsey states the basics. 

1.       Gammon value is 1.0.  Go for the gammon if risky play wins more gammons than extra losses.

a.       (i.e. extra gammons > extra losses)

2.       Leader Wants

a.       Gammon-free game (Race, Holding Game)

b.      Advanced anchor

c.       Think defense first

d.      Opening moves are gammon-save

3.       Trailer Wants

a.       Gammonish positions (Blitz, Prime, Backgame)

b.      Think Offense first

c.       Opening moves are gammon-go

Stick Rice goes into more detail in his Gammon Village article.  Note I don't know if I am interpreting the nactation and bot figures correctly.


A match score is Gammon Go if gammon value is 1.0, gammon losses are no more costly than single losses, and the opponent holds a dead cube.

GG applies to these scores:

1.       2 away Crawford

2.       2 away 4 away once cube is turned

3.       1 away 3 away post-crawford once cube is turned.

4.       1 away 4 away Crawford * (GV actually greater than 1 b/c value of free drop but whatever)

Note 3 away 4 away and 4 away 4 away are not Gammon Go!  While the GV is almost 1.0 for the trailer, gammon losses still cost and also the cube is not dead for the leader.

The key to checker play at gammon go is the dramatic increase in the value of a gammon to the trailer.

·         In a money game, a risky checker play is worth it if you win twice as many gammons as plain losses. (or  GV = .5)

·         At Gammon Go, a risky checker play is worth it if you win as many gammons as plain losses (or GV = 1.0)

Opening Play

1.       Opening Rolls

a.       Point Rolls: [61, 53, 42, 31, 64]

                                                               i.      Always make a point

                                                             ii.      64P is clear b/c of the extra gammons

b.      Split or Two-down Rolls: [54, 52, 53, 32]

                                                               i.      Always play two down to capture the gammons

c.       Slot or Split Rolls: [21, 41, 51]

                                                               i.      Always slot to capture the gammons

d.      Other Rolls: [65, 63, 62]

                                                               i.      65.  Run still best but splitting isn’t terrible

                                                             ii.      63.  Split is best.

                                                            iii.      62.  Split and Slot are tied.  (Note 62$ is .05 error for money)

2.       Reply Rolls  (examples from article with explanation)

a.       31P-21

                                                               i.      Slotting (13/11, 6/5) is slightly better than splitting (23/23, 13/11)

                                                             ii.      Note 21$ will be MORE correct as reply to other point making rolls, since opponent will have a weaker point and greater race lead!

b.      61P-Non point making aces [21, 41, 51]

                                                               i.      Always slot

c.       52S-54

                                                               i.      Attack with 13/9, 8/3* to deny the advanced anchor and maybe get a blitz going

3.       Reply Rolls (examples from with answers in NacBracs)

a.       21S-21 g [$ S11] /10

                                                               i.      Slot 13/11, 6/5 best. 

                                                             ii.      Split 24/23, 13/11 small error .011

b.      21S-33 g [A N18 B18] /5

                                                               i.      Attack 8/5(2), 6/3(2) best

                                                             ii.      Near 13/10(2), 6/3(2) small error .018  

                                                            iii.      Both 24/21(2), 13/10(2) small error .018

c.       21S-65 g [S R17] /5

                                                               i.      Attack 13/7, 6/1* best

                                                             ii.      Run 24/13 small error .017

d.      21$-33 g [A C31 B35] /5

                                                               i.      Attack 8/5(2), 6/3(2) best

                                                             ii.      Cross 24/21(2), 8/5(2) medium error .031

                                                            iii.      Both 24/21(2), 13/10(2) medium error .035

e.      41S-33 g [A B3 E16] /5

                                                               i.      Attack 8/5(2), 6/3(2) best

                                                             ii.      Both 24/21(2), 13/10(2) tied .003

                                                            iii.      Each 24/21(2), 6/3(2) small error .016

f.        41S-63 g [X S3 R20 H20] /5

                                                               i.      Hit & Split 24/21, 8/2* best

                                                             ii.      Split 24/18, 13/10 tied .003

                                                            iii.      Run 24/15 small error .02

                                                           iv.      Hit 13/10, 8/2* small error .02

g.       41S-65 g [S H3 R13 h24] /15**5

                                                               i.      Split 24/18, 13/8 best

                                                             ii.      Hit 13/7, 6/1* tied .003

                                                            iii.      Run 24/13 small error .024

                                                           iv.      Hit & Split 24/18, 6/1* small error .024

h.      32S-44 g [A C19] /5

                                                               i.      Attack 8/4*(2), 6/2(2) best

                                                             ii.      Cross 24/20(2), 8/4*(2) small error .019

i.         52S-63 g [H R34 S43] /5

                                                               i.      Hit 13/7, 6/3* best

                                                             ii.      Run 24/13 medium error .034

                                                            iii.      Split 24/18, 13/10 medium error .043

j.        62S-33 g [o n22 P26] /5

                                                               i.      o 24/18, 13/7* best

                                                             ii.      n 13/7*, 8/5(2) small error .022

                                                            iii.      P 13/7*(2) small error .026

k.       43S-61 g [H X9 P62] /15**5

                                                               i.      Hit 13/7, 6/5* best

                                                             ii.      Hit & Split 24/18, 6/5* tied .009

                                                            iii.      Point 13/7, 8/7 blunder .062

l.         43S-65 g [S $14] /5

                                                               i.      Split 24/18, 13/8 best

                                                             ii.      Slot 13/7. 13/8 small error .014

m.    53P-41 g [$ S4] /5

                                                               i.      Slot 13/9, 6/5 best

                                                             ii.      Split 24/23, 13/9 tied .004

n.      65R-62 g [D $14 S16] /5

                                                               i.      Two Down 13/11, 13/7 best

                                                             ii.      Slot 13/5 small error .014

                                                            iii.      Split 24/18, 13/11 small error .016

o.      65R-65 g [H D0.5 S2.5 R25] <62**41

                                                               i.      Hit 13/7, 6/1* best

                                                             ii.      Two Down 13/7, 13/8 tied .005

                                                            iii.      Split 24/18, 13/8 small error .025

                                                           iv.      Run 24/13 small error .025

Margins are in thousandths.

Score Before the brackets:  d = dmp, g = go; else assume money.

Bot and Trials after the brackets:  (~ Snowie, / GnuBG, < XG 3-ply, ^ XG 4-ply) and the number of trials, in thousands (rounded down).
For example, "g[S U16] /5" means that at (gammon) go, S is best and U is -.016 in a GnuBG rollout of 5000+ trials

Nactation Key:
D = Down (from the midpoint, usually with two checkers).
H = Hit on highest point possible. If H describes only half the roll, the other half comes down (e.g., for 32S-43, H means 13/10 8/4*).
K = Kill: hit twice.
P = Point on head if possible, or make the strongest offensive point available.
R = Run (to the outfield) with one checker. Exception: for 64S-44, R means run both checkers (i.e., 24/16(2)).
$ = Slot. Move one checker down from the midpoint and use it or another checker to slot the 5pt or 4pt (unstacking the 6pt when possible).
S = Split the back checkers and bring one checker down from the midpoint. S sometimes hits incidentally.
Z = Reverse split. When more than one splitting play is possible, Z splits with the small number and comes down with the large number.
U = Up with two back checkers. Exception: with a roll of 21, U brings up only one checker (i.e., 24/21).
W = Wild. Split with the large number and slot the 5pt or 4pt with the small number.
X = Hit and Split.
4 = Make the 4pt, or (in the case of 43U-63) hit on the 4pt.
Mostly for Doublets: ("beacon")
A = Attack. Make two inside points. Example: for 41S-55, A means 8/3(2) 6/1*(2)).
B = Both. Move up and down, making an anchor and an outer point. Example: for 32D-44, B means 24/20(2) 13/9(2).
C = Cross. Cross the bar — making an offensive point, and make an anchor. Example: for 51$-33, C means 24/21(2) 8/5(2).
E = Each. Make a point in each inner board. Example: for 54D-22, E means 24/22(2) 6/4(2).
e = each (variant). Split and make an inside point. Example: For 21S-11, “e” means 24/22 6/5(2).
N = Near. Move half the roll to/within each near-side quadrant (inner board, outer board). Example: for 62S-11, N means 8/7*(2) 6/5(2).
O = Outer. Half of play into the outer board and half out of the outer board. Example: for 61P-66, O means 13/7(2) 8/2(2).
Later Game Play

Examples where big plays that you’d never make in a money game are correct at the Gammon Go score.  The theme, of course, is to capture those gammons.

Rather than cover and make a clean 5 point board, it was correct to hit loose instead with a 4 point board and two slotted blots!

Greedy bear-offs can often be right, even volunteering a shot to capture the extra gammons.

1 comment:

  1. "4. 1 away 4 away Crawford * (GV actually greater than 1 b/c value of free drop but whatever)"

    Should read: post-crawford

    "b. Split or Two-down Rolls: [54, 52, 53, 32]"

    Should be 43 instead of 53

    "c. 21S-65 g [S R17] /5
    i. Attack 13/7, 6/1* best"

    Should read "Split 24/18, 13/8 best" (unless the nacbracs are wrong)