Backgammon Glossary

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 10-Percent Doubling Rule A guideline for cube handling in pure race positions. If you add 10% to your pip count, you should double if the result is not more than two pips greater than the opponent's count, and you should redouble if the result is not more than one pip greater. Your opponent should accept the double if your count plus 10% is no more than two pips less than his count. 8-9-12 Doubling Rule A guideline for cube handling in pure race positions. You should double if the opponent's pip count exceeds yours by 8% or more, and redouble if it exceeds yours by 9% or more. Your opponent should accept the double if his pip count exceeds yours by no more than 12%.

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 Early Game The first few moves of a game, before the players have settled on a particular game plan. Early-Late Ratio A comparison of the cost of doubling slightly before opponent's drop point versus doubling slightly past opponent's drop point. This number varies depending on the score of the match, the level of the cube, and the chance of gammon in the current game. It is useful in determining how aggressively a player should double to avoid losing his market. See post by Tom Keith. Edge of a Prime The open point directly in front of a prime. Effective Pip Count The average number of rolls required to bear off all your checkers multiplied by the average pip value of a roll (49/6 pips). A player's EPC is equal to his actual pip count plus the wastage of the position. For more information, see article by Walter Trice and post by Douglas Zare. The EPC is also known as the Trice Count in honor of Walter Trice (1949–2009). Efficient Double A double made at or near the point of maximum effectiveness, when the opponent would be correct to either accept or refuse. Eject To abandon an ace-point game to avoid losing a backgammon (2) or a gammon. Elimination Format A tournament event in which half the competitors are eliminated each round until just one player remains.  Compare: Round Robin Format. Elo Ratings System A method of rating players devised by Arpad Elo for the U.S. Chess Federation in 1960. Most backgammon ratings systems are based on Elo's method; for example, see FIBS rating formula. EMG Equity Equivalent-to-money-game equity. End Game The phase of a game which starts when either player begins to bear off. Enter To move a checker from the bar to an open point in the opponent's home board according to a roll of the dice. When a player has a checker on the bar, this is his only legal move. EPC Effective pip count. Equity The value of a position to one of the players. Equity is the sum of the values of the possible outcomes from a given position with each value multiplied by its probability of occurrence. It is the same as the fair settlement value of the position. Your equity is the negative of your opponent's equity. See post by Gary Wong. Equity comes in different flavors.  See: Cubeless Equity, Cubeful Equity, Match Equity, and EMG Equity. Equivalent-to-Money-Game Equity Cubeful equity normalized by transforming it linearly so that winning a single game at the current value of the cube is reported as +1 and losing a single game at the current value of the cube is reported as −1. EMG equity is commonly used in match play to compare the size of errors in different games. See the Snowie Support FAQ for a further description and an example. ER Backgammon ER stands for Error Rate. Playing ER backgammon means playing with a view to making the least errors from the outset rather than deliberately making suboptimal plays to steer the game toward a position that your opponent will misplay or doesn't understand. Error Rate A measure of the average equity lost per move due to errors in play. The lost equity can be measured either in match-winning chances or EMG equity. Different programs compute error rate differently: Snowie divides by the total number of moves and reports the rate in "millipoints per move." Gnu Backgammon divides by the number of unforced plays. See post by Gregg Cattanach. Escape To advance a runner to safety or past the opponent's blockade. Establish a Point Make a point. Eureka [Also spelled "Eureika".]  Simplified backgammon, in which each player starts with two checkers on his one, two, and three-point, and three checkers on his four, five, and six-point. See How to Play Eureika. Exposed Checker A blot within range of a direct hit. Extras See: Mandatory Extras. eXtreme Gammon A neural-net backgammon program introduced in 2009.   Website: eXtreme Gammon.

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 Illegal Move A move that does not conform to the roll of the dice as defined by the rules of backgammon. An illegal move must be corrected if requested by the opponent before the opponent rolls the dice to begin his own turn.  See: Illegal Moves Rule. Illegal Moves Rule The standard rule in backgammon which says: If a player makes an illegal play, the opponent has the option of allowing the error to stand or requesting that it be corrected. He must make this request before rolling the dice to begin his own turn. Once a correction is requested, the illegal mover is free to make any legal play he chooses.  Compare: Legal Moves Rule. Illegal Play A play that does not conform to the roll of the dice as defined by the rules of backgammon. An illegal play must be corrected if requested by the opponent before the opponent rolls the dice to begin his own turn.  See: Illegal Moves Rule. Illegal Position A position which cannot be reached through any sequence of legally played rolls. For example, both players closed out with checkers on the bar is an illegal position. Illegal positions are not allowed under the rules, and any misplay that creates an illegal position must be corrected. Inactive Builder A checker that is presently part of a prime or a block but which has the prospect of being used later to make another point. Indirect Hit A hit that uses the numbers on both dice taken together.   Compare: Direct Hit. Indirect Shot An opportunity to hit an opposing blot using the numbers on both dice taken together; a combination shot.   Compare: Direct Shot. Initial Double A double offered while the cube is still in the center, as opposed to a redouble where the player making the double has possession of the cube. Initial Stake The amount initially wagered in a game of backgammon (1). At the end of the game, this amount is multiplied by the final value of the doubling cube, and further multiplied by 2 if the win is a gammon or 3 if the win is a backgammon (2). Initiative A term used to describe a situation where one player has relative freedom to build his position or attack the opponent as he chooses, while the other player is reduced to making forced plays and trying to stave off disaster. The first player is said to have the initiative. Inner Board Home board. Inner Table Home board. Intermediate Division A division of a tournament designed for players too strong for the novice division and who do not wish to compete in the open division. Intermediate Level A player of some experience who has begun to hone his skills; the level of play between novice and advanced. In the Air On the bar. Irish A sixteenth-century game popular in England and other European countries, and probably backgammon (1)'s direct ancestor. Rolls of doubles are played just like any other roll, and there are no gammons or backgammons (2).  See: How to Play Irish.

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 Jackpot A elimination event, usually with a large entry fee, in which only the winner and runner-up receive prize money. Jacoby Paradox [Named for Oswald Jacoby, who mentioned it in The Backgammon Book, page 116.]  The fact that an improvement in the opponent's position can make redoubling correct in a position in which the player on roll owns the cube and has one remaining chance to redouble. Jacoby Rule [Named for Oswald Jacoby, who proposed the rule.]  A rule popular in money play which says that gammons and backgammons (2) count only as a single game if neither player has offered a double during the game. The Jacoby rule is not used in match play. The rule speeds up play by eliminating situations where a player avoids doubling so he can play on for a gammon. See post by Daniel Murphy. Jacquet A game once popular in France in which players start at diagonally opposite corners and move around the board in the same direction.  See: How to Play Jacquet. Janowski's Formula A formula devised by Rick Janowski for estimating match equity (1) at a given score. If d is the difference in match score and t is the number of points (4) the trailing player has to go, then the probability of the leading player winning the match is .5 + .85d / (t+6).  See also: Neil's Numbers and Turner's Formula. Janowski's Formulas A collection of formulas devised by Rick Janowski for estimating cubeful equity from cubeless equity. The basic formula for cubeful equity (between take points) is: ` CF = CL*(1 - x) + CE*x` where CF is cubeful equity, CL is cubeless equity, CE is cubeful equity assuming all doubles are perfectly efficient, and x is a number between 0 and 1 that measures the cube efficiency. Typical values for x range from 0.55 to 0.8.   See also: Janowski's Takepoint Formula. Janowski's Takepoint Formula A formula devised by Rick Janowski for estimating your take point given your cubeless probability of winning the game. The basic takepoint formula is: ` 2L - 1 TP = ----------- 2W + 2L + x` where TP is the cubeless equity of your take point, L is the average value of your cubeless losses (e.g., −1, if you can't lose a gammon), W is the average value of your cubeless wins (e.g., +1 if you can't win a gammon), and x is a number between 0 and 1 (typically 0.55 to 0.8) that measures cube efficiency. See Janowski's article, Take-Points in Money Games. Jellyfish The first commercial neural-net backgammon program (1994) after TD-Gammon.   Website: Jellyfish Backgammon. Jeopardy Potential for awkward rolls on a future turn.  See also: Double Jeopardy. Joint Standard Deviation The standard deviation of the difference between two rollouts: JSD = sqrt(SD1*SD1 + SD2*SD2). A measure of how statistically significant the result is. Joker An exceptionally good roll, especially a roll that reverses the likely outcome of the game; a roll much luckier than average. JSD Joint standard deviation. Junior Affectionate name for a player's farthest-back checker.

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 Odds The ratio of the probability of an event happening to that of its not happening, or vice versa. Usually the higher number is given first. For example, the odds of rolling double 6's are "35 to 1 against". Off (the Board) Said of checkers which have been borne off. One-Checker Model A model for estimating winning chances in a pure race based on the players' pip counts. In this model, all of a player's pips are represented by just one checker on a infinitely-long backgammon board. The one-checker model overestimates winning chances in positions where one side has more wastage than the other. See post by: Hugh Sconyers. One-Point The deepest point (1) in a player's home board, the point farthest from the bar and closest to being borne off; also called the ace-point. One-Point Match A backgammon variant where the goal is to be the first player to bear off all of your checkers. There is no doubling cube and no bonus for gammons or backgammons (2). Since you never lose more than one point (4), back games are more of an option in this variant than in regular backgammon. See posts by Lou Poppler and Bernhard Kaiser. One-Sided Bearoff Database A bearoff database where the arrangement of checkers on only one player's side is considered. The values in the database are calculated assuming the goal at each turn is to minimize the average number of rolls required to bear off.  Compare: Two-Sided Bearoff Database. Online Backgammon This refers to playing backgammon over the Internet. Online backgammon allows players all over the world to compete against one another. You can play for rating points or for real money.  See: Backgammon Server. On Roll The player whose turn it is. You are on roll as soon as your opponent picks up his dice to end his turn, and before you throw the dice to begin your own turn. For example, the only time you may double is when you are on roll. On the Bar Where a checker is placed after it is hit. When you have a checker on the bar, you may not move any of your other checkers until that checker has been entered back onto the board. On Tilt Steaming. Open Division The main division of a tournament; the division that any player may enter. Also called the championship division, it generally has the highest entry fee, the largest prizes, and attracts the strongest players.  Compare: Novice Division and Intermediate Division. Opening Game The first phase of a backgammon game where the players have yet to establish their initial game plans.   Compare: Middle Game and End Game. Opening Roll The first roll of the game in which both players simultaneously roll one die. This roll determines both the player to go first and the numbers that player must play. Open Point A position on the board not occupied by two or more of the opponent's checkers. Open Tournament A tournament open to any player regardless of strength or experience.  See: Open Division. Optional Reroll Rule California rule. OTB Over the board. Otter [Another furry rodent, by analogy to beaver and raccoon.]  An immediate redouble (while retaining ownership of the cube) by the player who just accepted a raccoon. Outer Board The side of the board away from where the players bear off their checkers. Each player's outer board comprises that player's points seven through twelve.  Compare: Home Board. Outer Table Outer board. Outfield The outer board, particularly points nine, ten, and eleven. Outside Prime A contiguous sequence of blocked points in which the majority of those points are in the outer board. Overage Points (4) won in excess of those needed to win a match. For example, if you win a game worth 4 points in a match in which you are 2 points away from winning, the surplus 2 points are overage. Overplay Make an unnecessarily big play. Over the Board Games played face-to-face, as opposed to on the Internet or by correspondence. Own a Point To have two or more checkers on a point (1) so that the opponent is blocked from landing or touching down there. Owner of the Cube The player who last accepted a double in the game. He places the cube on his side of the board to indicate that only he may make the next double.  See: Cube Ownership. Own the Cube The player who last accepted a double is said to own the doubling cube. He places the cube on his side of the board. Only the owner of the cube may offer the next double in the same game.  Compare: Centered Cube.

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 Quacks Double ducks. Quadrant One quarter of the playing area on a backgammon board. The first quadrant comprises a player's points 1 to 6, the second quadrant points 7 to 12, the third quadrant points 13 to 18, and the fourth quadrant points 19 to 24. Quads The roll of 4-4 on the dice (double 4's). Quarter Entry A quarter entry is a single elimination tournament for four players, which is held before the beginning of a greater tournament. Each of the four contestants pays an entry fee of (usually slightly more than) a quarter of the entry fee of the main event. The winner of this four person tournament is entitled to play in the main event. Quasi-Random Dice A technique used to reduce the element of luck in a rollout by ensuring the numbers rolled in the first few rolls of each trial are as evenly distributed as possible. For example, if you roll out a position 36 times, quasi-random dice will ensure that each trial begins with a different roll. Quatre-Point Traditional name for the four-point. Quiet Play An unassuming play that does not hit, or slot, or pose an immediate threat; it just maintains the status quo. Quiz Factor A feature of a problem that makes it interesting enough to appear on a quiz. The mere appearance on a quiz suggests that the "obvious" play may not be the correct play.

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 Underdog The player judged most likely to lose a game or match.  Compare: Favorite. Underplay To make a safe, unnecessarily timid play when a stronger, more aggressive play is available. Under the Gun A blot in the opponent's home board which is within direct range of three or more of the opponent's builders and therefore in danger of being pointed on. United States Backgammon Federation (USBGF) A not-for-profit organization devoted to advancement of backgammon in the United States.   Website: usbgf.org. Unlimited Game Backgammon played using a doubling cube without any limit to the number of doubles and redoubles. Unlimited games are similar to money games, but are played without the Jacoby rule, beavers, or automatic doubles. In contrast, limited forms of backgammon include: match play and table stakes. Unstack To remove checkers from a heavy point.

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 Variance (of a Rollout) Level of random error in a rollout. Variance Reduction Any technique for reducing the random error of a rollout. Examples are: quasi-random dice, duplicate dice, and luck reduction. Luck reduction, a variance reduction technique that involves adjusting each trial's result based on an estimate of the luck associated with the rolls of the trial. Because luck reduction is by far the most effective technique for variance reduction, the term variance reduction is often used specifically to refer to this method. See posts by Jim Williams and David Montgomery. Variant Any game other than backgammon (1) which can be played on a backgammon board. Most backgammon variants use rolls of the dice to determine how the players' checkers move, just as in backgammon.  See: Backgammon Variants. Vidos The Greek name for the exact equivalent of Western backgammon. Greek backgammon, called portes, is slightly different than vidos in that it is played without a doubling cube and has no bonus for winning a backgammon (2). Vig Vigorish. Vigorish The small additional considerations that affect the total equity of a position, such as gammon vigorish and recube vigorish. Volatility A measure of how much a position's equity is likely to change in the next roll or two. See posts by Chuck Bower and Kit Woolsey. Voluntary Double A regular double, where one player offers to double the stakes of the game, as opposed an automatic double when identical numbers are thrown at the beginning of the game. Volunteer a Shot Purposely leave a blot within range of being hit now rather than be forced to leave it later when the danger may be greater.

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 Walk a Prime Roll a prime. Ward Count A formula devised by Jeff Ward for making cube decisions in pure race games. It is a modification of the basic pip count designed to take into account elements of checker distribution. Each player's Ward count is his pip count, plus 2 for each checker more than 2 on the one-point, minus 1 for each extra home-board point compared to the opponent, plus 2 for each extra checker on the board compared to the opponent, plus 1/2 pip for each extra checker outside the home-board compared to the opponent. Then the player on roll increases his count by 10 percent. Ward advises: Double if your count does not exceed the opponent's by more than 2; redouble if your count does not exceed the opponent's by more than 1; accept the double if your count does not exceed doubler's by more than 2 in a short race (50 pips), 3 in a medium race (75 pips), or 4 in a long race (100 pips). See post by Marty Storer. For a comparison with other methods, see the article, "Cube Handling In Noncontact Positions". Wash A blitzing (1) technique that involves switching points to hit an opposing blot. ["Wash" the slate clean.]  A settlement for zero points. Wastage The expected loss in pips (2) from dice rolls not fully utilized during bearoff. Wastage is calculated as W = R x 49/6 − PC, where R is the expected (average) number rolls required to bear off, and PC is the pip count of the position. Wastage is the difference between the usual pip count and the effective pip count. See post by David Montgomery. WBA World Backgammon Association.  Website: WBA. WBF Worldwide Backgammon Federation.  Website: WBF. Weaver Coup A ploy which may be attempted when you are playing on for a gammon and the opponent gets a lucky roll. You offer to double even if your position is still too good, hoping the opponent will mistakenly accept. See this thread. Whopper A checker play (2) error or cube play (2) error which costs more than 0.1 points of EMG equity; a blunder. See post by Daniel Murphy. Wipeout Blitz (1). Wisecarver Paradox: A straight race position in which a given roll played correctly induces the opponent to correctly double while an alternate (inferior) play would prevent the opponent from correctly doubling. This can happen when the correct play produces a position of greater volatility. Wisecarever paradox positions are examples of a cube provocation plays. Woolsey's Law for Doubling A rule of thumb advocated by backgammon expert Kit Woolsey: "If you are not absolutely sure whether a position is a take or a pass, then it is always correct to double." See The Doubling Rule, by Kit Woolsey.

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 Zone of Attack [Or simply the "zone".]  Points 1 through 11 on your side of the board. The success of a blitz depends on the number of checkers you have in the zone. Usually 10 is enough to make a blitz worth trying.