Getting started
The language of the board
The gammonGo board is handled directly: there is no move button and no move menu. Everything is played on the checkers, the dice and the Cube themselves.
A move is built one step at a time. Until you have confirmed it, every step can be taken back: nothing reaches your opponent before you decide it does.
The two sides do not see the board from the same end. Yours is always the lower one, and your checkers travel towards your home board — the one they will bear off from.
The board below is a sandbox: the position is set once and for all, and nobody is playing on the other side. Try the gestures that follow on it — those, at least, that do not wait for an opponent: nothing there moves without you, and nothing you build on it is sent anywhere.
Black, at the bottom, is on roll, and all fifteen black checkers have reached the home board: this is an endgame. The roll is a 2 and a 6.
Dragging a checker to its destination
Put the pointer — or your finger — on a checker, and release on the point where you want it to go. The step is built at once, and the checker moves there.
The die consumed is the one that leads from the start to the arrival. A drag that matches no legal move does nothing — no message, no penalty: the checker stays where it was.
A point that holds a single opposing checker can be hit: the checker landing there sends the other one to the bar. On the sandbox, drag a checker from point 5 to point 3, where a white checker has been left alone.
Indicating a checker, without aiming at a destination
Put your finger on a checker and release it in the same place: the step is built without your having had to aim at anything. This is an indication.
The destination, this time, is chosen by the dice. The first die still available is used; if it can do nothing from that point, the next one is tried; if neither can, nothing is built.
The gesture works with a mouse too: a click without movement is a drag whose start and arrival are the same point, and the board does not tell the two apart.
Bearing a checker off the board
Once all your checkers have reached your home board, they may leave the board. The gesture is a drag, with the tray as its destination: take the checker, and release it on the hollow of the tray — the one where the checkers already borne off are stacked.
That hollow is drawn at all times, even when empty. It is a place where things are put away, not a landmark that would appear at the useful moment: nothing shifts when you start bearing off.
An indication can bear a checker off as well, when the die of the moment allows it. The drag to the tray, however, says so without ambiguity.
On the sandbox, drag a checker from point 6 to the tray: it is the 6 that bears it off.
Swapping the dice
A gesture that begins and ends on the dice — anywhere on them — swaps their order. It is not the indication of one die: it is a toggle, and making the gesture again restores the initial order.
It acts only where a choice exists: a playable board, no step built yet, a roll that is not doubles, and two distinct dice still playable. Everywhere else — a position read in the feed, a move already begun, doubles — the gesture does nothing.
The gesture has to begin and end on the dice. A drag that started from a point and was released on a die by mistake swaps nothing: no move is lost through clumsiness.
Rolling the dice
In a game, when it is your turn and the dice have not been rolled yet, a gesture on the dice rolls them.
It is the same gesture as the swap, in the same place: what tells them apart is the moment. Before the roll there is nothing to swap; afterwards there is nothing left to roll.
The sandbox does not offer it: manufacturing dice would be playing a game, and this page does not play. It is therefore learned from the text alone.
Picking up the dice to confirm your move
Building a move does not send it. Once it is complete, a gesture on the dice confirms it and passes it to your opponent: this is called picking up the dice.
The move has to be complete: while a die is still to be played, picking up does nothing and the dice stay where they lie. Nothing leaves before this gesture. Once the dice are picked up, however, the move is played.
Like the roll and the swap, it has to begin and end on the dice.
The sandbox does not offer it: there is nobody there to send a move to.
Taking back a step
A step is taken back by making it in reverse: take the checker you have just played, and release it on the point it came from.
The gesture undoes the last step only. To take back an older one, repeat it: you go back up one step at a time.
With a mouse, a right-click on the board takes back the last step without your having to aim at the checker.
A checker borne off is taken back the same way: pick it up in the tray, and release it on the point it had left.
On the sandbox, drag a checker from point 5 to point 3 — the white checker goes to the bar —, then bring it back from point 3 to point 5: the white checker returns to its point.
Doubling: offering the Cube
A gesture on the Cube offers to double the stakes. It happens in two stages, and the first sends nothing.
First stage: a large Cube appears at the centre of the right half of the board, ringed with a halo. It carries the offered value — twice the current one —, never the value of the moment.
Second stage: a gesture on that large Cube sends the offer.
To go back, a right-click on the board withdraws the offer, and the Esc key does the same. The large Cube disappears, and nothing has been sent.
The sandbox does not offer it: with no opponent, there is nobody to offer anything to.
Taking the double
When your opponent doubles, that same large Cube appears at the centre of the right half of the board, carrying the offered value. A gesture on it accepts.
One stage here, not two: the Cube is already displaced. You are answering a question that has been put.
During this decision, no checker can be played: the board only serves to answer, and the other answer is the next gesture.
The sandbox does not offer it either: nothing is decided there.
Dropping the double
The other answer is painted on the board during the decision, and only then: a zone marked “Drop”, at the centre of the left half. A gesture on it ends the game.
The zone covers points, harmlessly: during a Cube decision, no checker is played. It never covers the trays — a gesture on the dice or on the score stays what it is.
Once the decision is past, the zone no longer exists: the place becomes ordinary board again.
What dropping costs is read at “The Cube”.
Notation
A position is looked at, but a move is written. Notation is that written language: it is what the analysis panel ranks candidate moves in, what a transcript records a game in, and what your answers are compared in. It comes down to a handful of signs, and once they are read, the whole rest of the product reads with them.
Points are numbered 1 to 24 starting from your home board: your point 1 is the one your checkers bear off from, your point 24 the one they set out from. Your opponent counts the other way round, so the same point carries two numbers depending on which side is naming it.
Everyone therefore always writes their moves in their own numbering, and a move can only be read knowing whose it is: the same 13/7 denotes two opposite journeys depending on the player who made it. One practical consequence: within a written move, the arrival number is always smaller than the starting number, since a checker advances towards its home board and never the other way.
A step is written start/arrival. 8/5 brings a checker from point 8 to point 5. A complete move lines up its steps separated by a space: 8/5 6/5 moves two checkers, one from 8 to 5, the other from 6 to 5. The order of the steps in the line carries no meaning — 8/5 6/5 and 6/5 8/5 are the same move, and the product recognizes them as such.
Two words take the place of a point number. bar is the bar, from which a checker that has been hit re-enters play: bar/20 re-enters a checker on point 20. off is the exit, where a checker leaves the board for good: 6/off bears a checker off point 6. Neither is ever an intermediate stage — one only ever leaves from the bar, and only ever arrives at off.
A star marks a hit: 6/1* says that the checker arriving on point 1 found a lone opposing checker there and sent it to the bar. The star qualifies the step, not the whole move: in 13/11 6/1*, only the second step hits.
A number in parentheses repeats the same step that many times. 13/11(2) moves two checkers from point 13 to point 11, and is written that way rather than 13/11 13/11. The common case is doubles, where all four steps have the same length: 13/11(2) 24/22(2) is a complete move played with double 2s.
A single checker that travels both dice may be written in one stretch. With 4 and 3, a checker going from point 10 to point 6 and then to point 3 is written just as well 10/3 as 10/6 6/3: it is the same move, only condensed. The product reconciles the two spellings for you, but it is worth knowing that an analysis line may use one where the board had you build the other.
Finally, a turn where no step is possible carries no segment at all: the line is empty. Depending on the source the match comes from, it may instead carry the mention cannot move or dance.
The Cube
The Cube is a die apart, one that is never rolled. It sits at the side of the board and carries a number: the value of the game in progress, in points. At the start of a game that number is 1. The Cube makes nobody win — it multiplies what the game earns for whoever wins it.
Its position on the board says who it belongs to — there is no label to read beside it. In the middle it belongs to nobody, and both players may use it. Put away on one player's side, it belongs to that player: from then on, they alone may use it.
To double is to offer to multiply the value of the game by two. You may only do so on your turn, before you have rolled the dice, and only if the Cube is in the middle or already belongs to you.
Your opponent then has only two answers. “Take”: the game is now worth double, and the Cube moves to their side — they alone will be able to redouble afterwards. “Drop”: the game stops at once, and they concede you the value it had before your offer. Dropping therefore never costs more than what was already at stake, and it is that ceiling that makes the decision computable.
The analysis panel names these choices somewhat differently from the board: it presents three options, “No double”, “Double, Take” and “Double, Pass”. Passing and dropping denote the same act, the one that ends the game rather than doubling what is at stake.
Two ways of ending a game multiply the stake further. If the loser has borne no checker off, the game is worth double: that is a Gammon. If they have borne none off and, on top of that, still have a checker in the winner's home board or on the bar, it is worth triple: that is a Backgammon. These factors multiply the value of the Cube — a Gammon won on a Cube at 4 is worth eight points.
In a match, one rule suspends the Cube for the length of a single game: the Crawford rule. The first game in which one of the two players is only one point away from winning the match is played without the Cube — nobody doubles in it. Once that game is past, the Cube returns for all the following ones, which are said to be post-Crawford.
The score painted on the board reads in the same spirit: it does not count the points won but those left to win. 5a reads five points to go; 1a therefore flags a player one point from the match, that is, the Crawford game; pc marks a post-Crawford game; and the symbol ∞ a game that belongs to no match, and whose points therefore count towards nothing.
Equity
Equity puts a number, in points, on what a position earns on average for the player on roll. Zero is perfect balance: both sides expect exactly the same from it. A positive number is to your advantage, a negative one to your opponent's.
The product always writes it signed and to three decimal places: +0.142, -0.087. The sign is never left out, not even in front of a positive number. The search filters ask for the same quantity in millipoints, that is, in thousandths of a point: 0.142 is written 142 there.
Equity is not capped at one point. A plain game won is worth one point, a Gammon two, a Backgammon three, and the Cube multiplies the lot: an equity of +1.284 is therefore nothing out of the ordinary — it says that better than a plain win is expected on average.
One of these numbers on its own says almost nothing, though. What can be used is the gap. The analysis panel ranks moves by decreasing equity: the first line is the best move, and it is the one that measures all the others. From the second line on, a second number appears on the right — the difference from the best move. It is never positive, since nothing can be worth more than the best, and it is that number, never equity itself, that says what a choice has cost.
A line therefore reads from left to right: the rank, the move, its equity, then its gap. For instance, 2. 13/10 24/23 +0.105 -0.037 reads as follows: second candidate in the ranking, worth 0.105 point, that is 0.037 less than the first.
That gap the product qualifies with a glyph of at most two characters, borrowed from chess notation. Below 0.020, nothing is shown: the difference is too small to be worth a remark. From 0.020, ?! marks an inaccuracy. From 0.040, ? marks a mistake. From 0.080, ?? marks a blunder. A correct move therefore carries no sign at all — here, absence is the information.
The color that accompanies the glyph says nothing more than the glyph does: it doubles it for peripheral reading, it does not replace it. The degree is read from the glyph alone, including without telling the colors apart.
On a Cube decision, the same reading applies to three lines rather than to a ranking: “No double”, “Double, Take” and “Double, Pass”, each with its equity and its gap. The equity of “Double, Pass” is always +1, since dropping costs exactly the point at stake, no more and no less: it is not a measurement, it is a boundary. An equity of “No double” above +1 therefore says that the position is too good to double — doubling would make your opponent drop and would earn you less than playing on.
Below these lines, a table gives the chances: “Winning chances”, “Gammon” and “Backgammon”, for you and for your opponent. These chances are nested, not carved up: Gammons are already counted among the wins, and Backgammons among the Gammons. Adding them would give far more than a hundred. Only the first column shares out to a hundred: your winning chances and your opponent's always come to 100 %.