Match Play

Forum Archive : Match Play

2-away/4-away: Neil's rule of 80

From:   Neil Kazaross
Date:   30 June 2004
Subject:   "Neil's Rule of 80 at -4-2"
Forum:   GammOnLine

Garyo asked me to elaborate on what I call the rule of 80, I guess I'm
vain enough to call it "Neil's Rule of 80" since I've been using it for
years and haven't seen it mentioned by anyone prior to me. What is written
below may be quoted by other BG websites or newsletters as long as I am
given credit for it.

"The Rule of 80 is an easy method of determining whether the leader at a
score of -4-2 can take the offered 2-cube. If there are no gammons
possible, the leader's take point is 20%. He risks 10% ME to gain 50% ME
by taking. Therefore, if the trailer wins more than 80% of all games, the
leader should pass and concede 1 point.

Doubled gammons are obviously very costly to the leader at -4-2 since he
then loses the match exactly. The leader's gammon cost at this score is 1.
His ME difference between losing the game and losing a gammon is 50% which
is equal to the difference in ME from him winning or losing the game.
(Note that in a cubeless money game the gammon cost is 1/2)

Any gammons lost by the leader (multiplied by his gammon cost) must be
subtracted from his wins to yield his effective winning percentage. If he
wins 30% of the games, but loses 10% gammons, his effective winning
chances become 20% (due to the gammon cost of 1 which means to subtract
gammons at a value of 1 per) and he has a borderline drop/take. Therefore,
to determine if the leader can take the cube at -4-2 his percentage of
winning minus his gammons lost should exceed 20% for him to have a proper

Perhaps I should call this The Rule of 20, but I prefer to think from the
standpoint of the trailer in the match who is always looking to make an
aggressive double at this score. If the trailer's total games won plus his
total gammons won (BG don't matter) exceed 80% then the leader should pass
the cube. The reason I prefer to think from the standpoint of the trailer
is that he should be thinking of how often he can win the game and how
often he can win a gammon and use this info to make an aggressive double.
For example, lets assume a reasonably volatile position where the trailer
wins 55% total games and 15% gammons. This totals 70 which is way less
than 80, so the leader has a trivial take. However, if the trailer
determines that there are quite a few sequences which leave him having a
total well above 80 next turn (ie clear market loss), it is very likely
that he technically has a proper double.

Whether you choose to apply this as the Rule of 80(trailer's wins +Gs) or
the Rule of 20(leader's wins - Gs lost) is up to you"

Did you find the information in this article useful?          

Do you have any comments you'd like to add?     


Match Play

1-away/1-away: advice from Bernhard Kaiser  (Darse Billings, July 1995)  [Long message] [Recommended reading]
1-away/1-away: advice from Stick  (Stick+, Mar 2007)  [GammOnLine forum]
1-away/1-away: and similar scores  (Lou Poppler, Aug 1995) 
2-away/3-away: playing for gammon  (Tom Keith, Feb 1996) 
2-away/4-away: Neil's rule of 80  (Neil Kazaross, June 2004)  [GammOnLine forum]
2-away/4-away: cube strategy  (Tom Keith, Dec 1996) 
2-away/4-away: practical issues  (Mark Damish, Jan 1996) 
2-away/4-away: trailer's initial double  (Kit Woolsey, Jan 1996) 
3-away/4-away: opponent's recube  (William C. Bitting+, Feb 1997)  [Long message]
3-away/4-away: racing cube  (Bill Calton+, Nov 2012) 
3-away/4-away: tricky cube decision  (Kit Woolsey+, July 1994) 
3-away/4-away: what's the correct equity?  (Tom Keith, Sept 1997) 
4-away/4-away: take/drop point  (Gary Wong, Oct 1997) 
5-away/11-away: redouble to 8  (Gavin Anderson, Oct 1998) 
7-away/11-away: volatile recube decision  (Kit Woolsey, May 1997) 
Both too good and not good enough to double  (Paul Epstein+, Sept 2007) 
Comparing 2-away/3-away and 2-away/4-away  (Douglas Zare, Mar 2002) 
Crawford rule  (Chuck Bower, May 1998) 
Crawford rule  (Kit Woolsey, Mar 1997) 
Crawford rule--Why just one game?  (Walter Trice, Jan 2000) 
Crawford rule--history  (Michael Strato, Jan 2001) 
Delayed mandatory double  (tem_sat+, Oct 2010) 
Delayed mandatory double  (Donald Kahn+, Dec 1997)  [Recommended reading]
Doubling when facing a gammon loss  (Kit Woolsey, Jan 1999) 
Doubling when opponent is 2-away  (David Montgomery, Dec 1997) 
Doubling when you're an underdog  (Stein Kulseth, Dec 1997) 
Doubling window with gammons  (Jason Lee+, Jan 2009) 
Free drop  (Ian Shaw, May 1999) 
Free drop  (Willis Elias+, Oct 1994) 
Gammonless takepoint formula  (Adam Stocks, June 2002) 
Going for gammon when opp has free drop  (Kit Woolsey, Jan 1998) 
Going for gammon when opp has free drop  (Kit Woolsey, Apr 1995) 
Holland rule  (Neil Kazaross, Apr 2010) 
Holland rule  (Kit Woolsey, Dec 1994) 
Leading 2-away with good gammon chances  (Douglas Zare, Feb 2004)  [GammOnLine forum]
Match play 101  (Max Urban+, Oct 2009) 
Matches to a set number of games  (Tom Keith+, Oct 1998) 
Playing when opponent has free drop  (Gilles Baudrillard+, Dec 1996) 
Post-crawford doubling  (Scott Steiner+, Feb 2004) 
Post-crawford doubling  (Maik Stiebler+, Dec 2002) 
Post-crawford doubling  (Gus+, Sept 2002) 
Post-crawford mistakes  (Rob Adams, Sept 2007)  [GammOnLine forum]
Post-crawford/2-away: too good to double  (Robert-Jan Veldhuizen, July 2004) 
Slotting when opponent has free drop  (onur alan+, Apr 2013) 
Take points  (fiore+, Feb 2005)  [GammOnLine forum]
Tips to improve cube handling  (Lucky Jim+, Jan 2010) 
When to free drop  (Dan Pelton+, Oct 2006) 
When to free drop  (Tom Keith+, July 2005)  [GammOnLine forum]
When to free drop  (Gregg Cattanach, Dec 2004)  [GammOnLine forum]
When to free drop  (Kit Woolsey, Feb 1998) 
When to free drop  (Chuck Bower, Jan 1998) 
Which format most favors the favorite?  (Daniel Murphy+, Jan 2006)  [GammOnLine forum]

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