Each domino has two ends, each showing a number. On this one we count 18 (green) and 12 (red) and therefore call it an eighteen-twelve. The difference between the two ends is 18 - 12 = 6, which is why we also call this domino a six-difference.
The dominoes can only be placed next to each other in such a way that the ends with the same number of points touch each other. So only a domino with an 18 or a 12 can be placed here.
Dominoes whose two ends show the same number are called doubles. These are always placed crosswise at one end with the same number of points. From such a piece, it is possible to continue in four directions.
The direction of play is in the manner customary in the country (for example, clockwise in Germany, counterclockwise in Switzerland).
The player whose turn it is places a domino at a suitable end. If she* cannot place a domino, she takes one from the stick and sits out, i. e. it is the next player's turn.
The numbers of the unoccupied ends are counted together. If the sum is divisible by the divisor (3, 5, 7, 9 or 11) determined according to the game without a remainder, the player receives the value of the quotient. Example: in the double eighteen, the divisor is 11; the player increases the sum of the ends to 110 with her domino. This results in the value 10 divided by 11 - thus the player is credited with 10 points.*Although the female form was chosen in the text for reasons of readability, the information refers to members of all genders.
The various well-known domino sets are played according to the following system:
The players sort their dominoes according to their differences in order to be able to react quickly to what is happening in the game at any time.
Differences can be grouped. If, for example, the divisor 7 is played, the differences 1 and 8, 2 and 9, 3 and 10, 4 and 11, 5 and 12 have the same effect, i.e. if a domino with the difference 3 can score, a difference 10 domino can also score. This is not magic, but is due to the fact that the 10 can be decomposed into the components searched difference (3) and played divisor (7).
When sorting, the difference of the divisor played should form the last row; for all larger differences, simply subtract the divisor and place the domino among the differences that the remainder gives. Example: the domino has the difference 9, played on divisor 7, therefore 9 - 7 = 2, therefore the domino belongs to the differences of two.
Doubles show the difference 0 (zero) but increase the sum of the ends by the number of one of their ends because of the cross-laying rule. A double four, for example, increases the total by four. Therefore, double dominoes can be sorted into the corresponding difference series.
The differences that together give the divisor played can also be grouped together. To stay with the divisor 7 example, differences of 4 and 3 can consequently be grouped. Because if it is possible to score with the increase by 3, it is also possible to score with the decrease by 4.
With the Daniela Ratzek sorting, where, for example, the 3-difference dominoes are placed from left to right upwards (the higher number of points on the right), and behind them the 4-difference dominoes are placed from left to right downwards (the higher number of points on the left), the overview of the respective game situation is optimised.
1st and 2nd move
Each player hides her dominoes from the others. Whoever has the highest double domino (depending on the game: double 6, ‑9, ‑12, ‑15, ‑18 or ‑21) opens the game by placing this domino on the table with the number of points facing upwards (1st move). If no one has the highest possible double domino, the player with the next highest double domino opens the game.
The next player in the direction of play places a domino with a matching number of points. To comply with the cross-laying rule for doubles, this second move is always made in such a way that there are three ends:
While the first player has put 36 points (two ends of 18) on the table with her double domino, the second player has added twelve points. So in this example there are three ends open, which are added together: 18 + 18 + 12 = 48. Therefore, if the double 18 is played on divisor 11 as intended, neither player 1 nor player 2 will receive points.
The third player now also wants to reach a sum divisible by the divisor 11. Starting from the first two moves with the sum 48, 55 would be the next higher and 44 the next lower number. To get from 48 to 55, a domino with the difference 7 is needed, which must also have a 12 or 18 as the smaller end (that would mean 12-19 or 18-25: but these dominoes do not exist in the double-18 set).
The next possibility would be the 18-7 domino, which would bring the total to 55 when placed as the fourth end to the double 18. However, this domino is a difference 11 domino and dominoes with the difference of the divisor are considered valuable for situations in which the previous player could score - a joker in the domino game, so to speak. Therefore, it would now only be placed if no other domino fits.
The last possibility is to reduce the sum by four, which requires a domino with the difference 4. The 12-16 would be such a domino - but placed at the 12, it increases the sum by 4! This would result in 52, i.e. no points, and so the 18-14 or 12-8 would be more suitable. The third player has such a domino, and so there are 18 + 18 + 8 = 44 points. That gives 44 ÷ 11 = 4 points for player 3!
Each player now tries to reach a sum divisible by the divisor. If the player whose turn it is does not succeed, she must still place a domino. If this is also unsuccessful, she sits out and has to pull a domino out of the stick – and it is the next player's turn.
Plus and minus
If you are afraid that you will have to add up all the ends throughout the game, don't worry. During the game, the sum is only changed by the difference between the two ends of the placed domino. For example, if you have the 18-8 domino, you have the difference of ten, because 18 - 8 = 10. If this domino is now placed at the end with the free 8, the total increases by ten - there are now 54 (if you count, you will find three ends with 18 points each):
However, if the same domino is placed at one of the two free ends with 18, the sum is reduced by ten - there are then 34 (three ends with 18 + 8 + 8).
When playing, two differences are always sought that either increase or decrease the sum in order to arrive at a number divisible by the divisor.
An exception are the doubles: their difference is zero and if they were laid out straight in line, they would not change the result. However, since they always have to be placed crosswise, one end of the corresponding number becomes two. This is also the reason why, for example, the double eight does not increase the sum by 16 (because of its two ends of 8), but only by 8.
Since the double domino covers the previously exposed end, the sum is first reduced by the covered 8 before the 16 are added. So you add up to ‑8 +16, which is +8. If this seems too complicated, just remember: double-eight makes plus eight, double-nine makes plus nine and so on.
Since doubles have to be laid crosswise, it is also possible to continue laying dominoes into the fourth direction, i.e. also to the fourth side that has not been used so far in our example. Since a new end is then opened without covering a previous one, the difference of the placed domino does not matter here - the total sum is simply increased by the number of the new end:
In this third way of putting the 18-8, the sum is 52 (four ends: 18 + 18 + 8 + 8).
End of game
As soon as a player has placed her last domino, the game is over. All the other players now add up the eyes on their remaining dominoes and subtract this result from the points they have scored so far. The winner is the player who has the most points after the deduction.
Match results submitted to FIDO are included in the calculation of the next world ranking. This takes place at the end of each month. The matches of the current month should therefore reach FIDO at the latest by the last day of the month. The player number FLADUB, which is calculated from the match results, ages and becomes visibly smaller until it is removed from the calculation after one year.
Submitted match results from previous months are of course also included in the calculation, but do not allow any more big jumps in the world ranking position.
The person entrusted by the round with the submission therefore takes on a great responsibility, since the world ranking of her fellow players also suffers if she oversleeps the monthly deadline.
Dominoes with the difference of the divisor played (so in the case of double 12, seven: 0/7, 1/8, 2/9, 3/10, 4/11, 5/12) as well as the double zero and double seven are valuable dominoes that can be used to score if the previous player has scored.
The same applies in this example (double 12 on divisor 7) to dominoes with a 0 or 7 end, which can possibly be placed as a fourth new end to the side of the matching double domino and thus either do not change the sum or even increase it by 7 (so-called tap-in or freeloader dominoes).
Each number is present in the game the same number of times. Doubles only have half a chance of being placed. The players should therefore keep an eye on how often "their" number is already present so that the double can be placed in time. It is similarly urgent to put down dominoes with a high number of points so that they do not burden the player with their deduction at the end.
It is advantageous to have dominoes of each type of difference in stock. In this way, there is a greater chance of being able to respond appropriately to all the previous player's moves. In the example of the double twelve game on divisor 7, the differences 1 and 6, 2 and 5, 3 and 4 can be used equally, i.e. if, for example, the previous player gives a total of 46, you can increase by 3 to 49 or decrease by 4 to 42 in order to score. Whoever manages to have dominoes from these difference pairs in stock until the end increases the chances of scoring.
Whoever opened the game will – if she did not have to draw a domino during the game – also end it. In this case, special care must be taken to ensure that all the dominoes can be discarded, while the other players, on the other hand, try to keep the domino with the lowest number of points as a discard domino. This can lead to a shortage of free ends with low numbers of points.
If you have a lot of dominoes from one number, you can possibly make the other players have to take up dominoes by constantly placing only this number as an open end (the Jokinen strategy) – but this can also become your own trap! The Bulgarian variant of this strategy achieved dubious fame and also contributed to the temporary disturbance of family peace.
If you do not have a matching tap-in domino, you should place something else on the fourth side of a double domino. This reduces the chances of the other players who probably have such dominoes and could use them accordingly (the ter Heide strategy). Juvente members at times cultivated this game variant to excess and without regard for their own losses.
In some regions of the world, this is explicitly forbidden, which is the reason for the Mother Theresa rule of mercy. In this other camp, excesses have already led to coffee cups being placed on dominoes needed by players in order to *reserve* them.
In response to the development of the Mother Theresa Rule, the Neumühl School agreed on the Schwerin Gentlemen Agreement. This form of full-contact domino is characterised by both polite recognition of the opponent and a Darwinian interpretation of the rules of the game. Unfortunately, this style of play – except perhaps still with Juvente – has not been able to establish itself on a large scale, as Mother Theresa simply scores more points.
The Neumühl school also introduced the Rostock knock, where after laying a double, the teammates knock appreciatively on the table. Whether this was to thank the teammate for bringing the total forward or to wake up teammates who had fallen asleep was never clarified beyond doubt.
The Basel wipe cancels that knock recognition if the laying of the double was not altruistic but used to score.
The Sönke Hansen strategy of not laying double dominoes across, but using them as a zero difference, has not caught on outside Büdelsdorf.
If a player discovers after the start of the game that she has drawn more dominoes than the others, these can no longer be returned. Their number of points is also deducted from the result at the end – if she discovers it early enough, she can of course make sure to keep the deduction low by keeping back those with a low number of points.
If a player has taken up too few dominoes at the beginning of the game, the missing dominoes must be drawn immediately – even if this is only discovered at the end of the game!
Cursing is generally encouraged during a FIDO game; Smoking and alcohol, on the other hand, are just as generally unacceptable (seeing doubles twice, after all, makes it difficult to play …).
Parliamentarians have to communicate their current world ranking position to the world public via the daily press (Lex Bölckow).