# Domino Rules

Rules as published by the Fédération Internationale de Domino (FIDO), as of the 29th of July 2005*. For short rules in norwegian please see this page or this page

## Basic Rules

A domino has two ends with each showing a number. Here to the right we count 18 (green) and 12 (red), what gives its name Eighteen-Twelve. The difference between these two ends is 18-12=6, what make this domino belonging to the group of difference-six.

Dominoes may only be played by putting ends with the same figure to each other. To continue here, we need a twelve or an eighteen. Dominoes with equal number on both ends we call doubles. They are always put across to an end with the same number. This allows to continue the game into four directions.

The direction of the game follows regional traditions (e.g. in Germany clockwise, while in Switzerland counter-clockwise, or how experienced pedagogues claim there: following the slap round the face...)

When it is a player's turn he puts a domino to a fitting end. If this is not possible he sits out and takes a domino from the stack and it is the next player's turn.

The figures of the ends showing open are added. If the result can be devided by the divisor according to the game (3, 5, 7, 9 or 11) without leaving a rest, the player earns the value of the quotient. Example: the double-18 is played on divisor 11; a player achieves the sum of 110 by putting his domino. Divided by 11, the player scores with 10 points.

Using the simple formula of (n+1)×(n+2)÷2 one can calculate the number of dominoes of a game by replacing n by the highest number. An ordinary double-six domino game in Germany has got six as highest figure. That means (6+1)×(6+2)÷2=7×8÷2=7×4= 28 dominoes. In Europe the double-9 is also known while in the USA double-12, double-15 and even double-18 are available.

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## Preparation

The different known domino games are played according to the following system:

Double-6 Double-9 Double-12 Double-15 Double-18
Number of dominoes in the game 28 55 91 136 190
Divisor 3 5 7 9 11
Dominoes per player with 3 Players 7 13 22 34 47
4 Players 5 11 18 27 38
5 Players 4 9 15 22 31
6 Players 4 7 13 19 27
7 Players 3 6 11 17 23
8 Players 3 6 10 15 21
9 Players 2 5 9 13 19

The players sort their dominoes by differences, in order to be able to react quickly in any game situation. When played e.g. on divisor 7, the differences 1 and 8, 2 and 9, 3 and 10, 4 and 11, 5 and 12 are similarly usable, what means if it is possible to score with a domino of difference 3, it will also work with one of difference 10. That is no magic but due to the simple fact that 10 can be split into the needed difference (3) and the divisor played (7). While sorting the difference of the played divisor forms the highest row; differences greater than the divisor will be reduced by the latter and belong to the group of the remaining figure. Example: the divisor is 7, the domino shows difference 9, so 9-7=2, the domino belongs to the group of differences 2.

Even showing difference zero, the doubles increase the sum of the ends by the number of one of their ends because they have to be put across. So a double-four increases the sum by four. That's why they are sorted together with the respective differences. And: doubles never decrease the sum.

Continuing the example of divisor 7, the dominoes with difference 3 may be sorted in the same line with difference 4. If it is possible to score with the increase by 3, scoring will also be possible with decreasing by 4. The attentive players will have noticed that the amounts of +3 and -4 give again 7.

The Daniela Ratzek system of sorting the dominoes, optimizes the overview of any game situation: the dominoes with difference 3 in a line, with the smaller number to the left, and behind them the dominoes with difference 4, with the greater number to the left.

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## Start of the game

Every player hides his dominoes from the other players. The player with the highest double of the game (according to the game: Double-6, -9, -12, -15 or -18) opens the game by putting it openly onto the table (1st move). If no one got that highest double, the player with the next highest double opens the game. The following player (in the direction of the game) puts a domino with a fitting number (with the 2nd move always) across, i.e. like this:

While the first player put 36 points on the table with his double here (two ends with 18), the second player added with his move 12. In this example there are now three open ends: 18+18+12=48. Since double-18 is played on divisor 11, neither the first nor the second player scored.

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## 3rd move

The third player wants to achieve a sum divisible by the divisor 11. The next higher number is 55, the next less 44. To achieve 55, a domino with difference 7 is needed with either 12 or 18 at one end (that means 12-19 or 18-25, but these combinations are not existing in a game of double-18).

The next possibility is the domino 18-7, which put to the left side opens a fourth end increasing the sum by 7. But this domino is a difference 11, and the dominoes with the difference of the divisor are holy, since they make it possible to improve a scoring move of the previous player. In real life, it will never be put now, except the case it's the only domino to move with.

The last possibility means to reduce the sum by four what requires a domino with difference 4. The 12-16 is such one, but put to the end of 12, it increases the sum by 4! That's not desired and the 18-14 or 12-8 are a better choice. The third player has got one of them, and now we count 18+18+8=44 points. Player no. 3 scores with 44÷11=4!

Everybody keeps trying to achive an amount divisible by the divisor. If the player at turn fails, he has to move any other domino. If that isn't possible either, he has to take one from the stack and sits out, and it's the next player's turn.

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## Up and down

One might be afraid of being forced to count all the time all these ends, but what actually happens is that the sum is just changed by the difference of the two ends of the domino moved. Example: with the 18-8 one got the difference 10; if moved to the right end, the sum increases by 10 - we count now 54 (three ends with 18):

 If the same domino is moved instead to the end of 18, the sum decreases by 10 - now we count 34 points (three ends with 18+8+8). While trying to achieve a sum divisible by the divisor, one can always try two differences.

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## Doubles

The doubles form an exception: their difference is zero and if moved in line they wouldn't change the sum. Since they have to be moved always across, they double the end. That doesn't mean that e.g. double-8 adds 16 (two ends of 8) to the sum. It only adds 8, because the former open end is closed when moving the double to it. So the sum decreases by 8 while adding the 16 of the double (-8+16=+8). If this looks too complicated, simply note: double-8 adds 8, double-9 adds 9 etc.

From the doubles the game can continue into four directions, i.e. also at the "naked" fourth side. By moving there, a new end is increasing the sum (no decreasing possible), and it's the only occasion when the difference of the domino is not valuable: simply the number of the new end will be added:

With this third possibility to move the 18-8, the sum is 52 (four ends 18 + 18 + 8 + 8).

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## End of the game

The game ends when a player has moved his last domino. The other players each count the points on their remaining dominoes and deduct the amount from their score. The player with most points after deduction wins the game.

All game results reaching FIDO will be entered into the calculation of the next world rankings, which takes place after each month. That means all results of a month shall arrive at FIDO on the last of the month . However, later arriving results still will be included in the following calculation, but the FLADUB formula values the latest games higher.That's why it's in every player's own interest to send in the results close after the date of playing, in order to achieve the best possible result in the world rankings.

The representative of the group accepts a great responsibility, since the world rankings of his team-mates also suffer, if he/she misses the deadline by oversleeping.

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## Tips to survive a game

Dominoes with the difference of the divisor (e.g. double-12 is 7: 0-7, 1-8, 2-9, 3-10, 4-11, 5-12) as well as double-0 and double-7 are valuable dominoes, which can be used to score, when the previous player scored. The same works with dominoes showing a 0 or 7, which might be moved to the »naked« fourth side of the double with the figure of their other end and thus either won't change the sum or increase it by 7 (the so-called scrounge or running board dominoes).

Each number is represented equally in a game. Doubles get half the chance to be moved. Each player should keep an eye on how often »his« number already has been moved, in order to get rid of the double in time. The same counts for dominoes with high numbers, which can be a burden at the end of the game when being deducted.

Try to keep as long as possible dominoes of each difference available, to be able to react on any of the moves of the previous player (keeping in mind the pairing of similarly working differences (1 and 6, 2 and 5, 3 and 4, when playing on divisor 7).

The player who started the game will most probably end it - if not being forced to take a domino from the stack during the game. While the others are interested in keeping the low numbers to the end in order to have low deduction from their score, the beginner must even get rid of a e.g. 0-1. The opposite interests of the players may lead to the situation that low figures run out when it comes to the end of the game.

A player who got the majority of one figure can try to force the other players to take dominoes from the stack by moving it to every end (Jokinen strategy) - but be careful not to fall into your own trap! The Bulgarian variation of this strategy became notorious for its temporary disruption of family peace.

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## Special rules

Players without scrounge dominoes should block the »naked« side of a double with any other domino to reduce the chance of those players in possession of these dominoes (ter Heide strategy). JUVENTE members follow this estrategy to excess regardless.

In some world regions exactly this is prohibited, which created the Mother Theresa rule of mercifulness. In this opposite camp some excesses, however, lead to strange behaviour, e.g. placing coffee cups on dominoes needed, in order to reserve them.

As a reaction to the Mother Theresa rule the New Mill Scool signed the Schwerin-Gentlemen-Agreement. This form of full contact domino distinguishes itself by polite acknowledgement of the opponent as a darwinistic interpretation of the rules. Unfortunately this way of playing didn't gain acceptance in greater scale - with the exception of maybe JUVENTE - since playing with Mother Theresa is obviously rewarded richer.

This school also introduced the Rostock knocking when the players knock on the table after a double has been moved. Whether to show gratitude for increasing the total amount or to wake up other players was never clarified beyond doubt.

The Sönke Hansen strategy to move doubles not across, in order to use them as difference zero, never won friends out of Büdelsdorf.

If a player after the beginning of the games discovers that he took more dominoes than the others, they will not be put back. Their points will also be deducted from the score.
If on the contrary he took not enough, the missing dominoes have to be taken on the spot - even when this first is noticed at the end of the game.

Cursing during a FIDO meeting is fundamentally welcome; smoking and drinking is as fundamentally inadmissible (seeing doubles double might impair the act of playing).

Parliamentarians are obliged to communicate their current world rankings position to the general public by means of daily press (Lex Bölckow).

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Rules copied from www.dominospiel.de on the 29th of July 2005.
Compilation and code simplification by Thomas Nygreen.