EP0354651B1

EP0354651B1 - Slot machine

Info

Publication number: EP0354651B1
Application number: EP89306274A
Authority: EP
Inventors: Yuji Nagao; Yoshihiro Kinoshita
Original assignee: Sigma Inc
Current assignee: Sigma Inc
Priority date: 1988-08-12
Filing date: 1989-06-22
Publication date: 1993-10-06
Anticipated expiration: 2009-06-22
Also published as: NZ229554A; MY105199A; JP2815587B2; AU610408B2; EP0354651A3; DE68909715D1; ES2047115T3; DE68909715T2; EP0354651A2; ATE95623T1; JPH0249681A; AU3643789A

Abstract

The present invention provides a slot machine for determining winning or losing by selecting predetermined symbols from symbol trains arranged on X reels, in accordance with a random number, in which the X reels have symbol trains of different numbers of symbols arranged thereon.

Description

The present invention relates to a slot machine which has X reels each provided with a plurality of symbols forming a so-called symbol train thereon or X symbol trains stored in a memory.
In playing such a slot machine provided with X mechanically driven reels, a player inserts a coin or token into a coin port provided in the slot machine body and manipulates a start lever or the like to cause the reels which have a plurality of symbols drawn on outer peripheries thereof to rotate. (Cf. e.g. US-A-4 037 845.)
Fig. 1 lists the symbols forming symbol trains provided on the reels of a prior art slot machine. It can be seen that the symbol train of each reel comprises the same number of symbols. Each symbol indicates a stop position of its reel and each symbol train consists of sixteen symbols which correspond to a stop position. Each symbol train includes four different symbols (7B, 5B, 1B, BL). combinations are (1) 7B-7B-7B, (2) 5B-5B-5B, and (3) 1B-1B-1B. The symbols which may form a winning combination of symbols are 7B, 5B and 1B and the winning combinations are (1) 7B-7B-7B, (2) 5B-5B-5B, and (3) 1B-1B-1B. The symbol train on the first reel includes the symbol 7B at a proportion of 2/16, the symbol 5B at a proportion of 2/16 and the symbol 1B at a proportion of 4/16. The symbol train on the second reel includes the symbol 7B at a proportion of 2/16, the symbol 5B at a proportion of 2/16, and the symbol 1B at a proportion of 3/16. The symbol train on the third reel includes the symbol 7B at a proportion of 1/16, the symbol 5B at the proportion of 2/16 and the symbol 1B at the proportion of 3/16. Accordingly, when the first, second and third reels are simultaneously rotated, a probability of occurrence of 7B-7B-7B is 4/4096, a probability of occurrence of 5B-5B-5B is 8/4096 and a probability of occurrence of 1B-1B-1B is 36/4096.
The outcome of a game, that is whether a player wins or loses, and where applicable the value of the win, is indicated by a combination of symbols appearing on a so-called winning line when the reels are stopped. The probability of winning in such a slot machine depends on the type and number of symbols arranged on the outer peripheries of the reels and the number of reels. In a recent slot machine, in order to maintain a pay-out rate at a predetermined level and to prevent extreme deviation of a probability of winning depending on technique, one random number is selected from a random number table in a given range, and the is determined on the basis of that random number.
In a typical three-reel type slot machine of the prior art, the selected random number is compared with a probability table to determine the outcome of a game and the symbols are selected by referencing symbol tables (one symbol table is provided for each reel) so that the game outcome may be displayed.
In another prior art slot machine, the selected random number is related to the symbols of the reels which are uniquely determined by the random number selected.
In these prior art slot machines in which the outcome of a game is determined by utilizing a random number, a problem occurs in that it is difficult to match the number of random numbers of a random number table to the number of combinations of symbols of the reels. For example, where 20 symbols are arranged on each of three reels and 8192 random numbers are derivable from a 13-bit binary number, a total number of combinations of symbols which may be generated for the respective reel stop positions is 8000, which is different to the total number of random numbers. As a result, even if a specific random number is selected at a uniform probability, two different random numbers are often assigned to some symbol combinations so that the probability certain game outcomes becomes substantially non-uniform.
In order to solve the above problem, JP-A-62-213782 disclosed a slot machine in which each of X symbol tables to be referenced when symbols are selected from symbol trains to determine the outcome of a game has Y Symbols equal to X-order root of 2ⁿ.
In this slot machine, a specific random number is sampled from 2ⁿ random numbers at the probability of 1/2ⁿ and the symbols of X symbol trains are determined based on the sampled random number. In this case, a probability in determining the symbols by referencing the symbol table is equal to the probability in sampling the random number (1/2ⁿ). Accordingly, the combination of symbols finally provided on the winning line is not biased and non-artificial natural game playing can be attained.
In the above slot machine, it is rare that the X-order root of 2ⁿ is an integer and a room for selection of the number Y of symbols arranged on the outer peripheries of the reels is narrow. For example, where 8192 random numbers derived from a 13-bit binary number and two reels are used, the number of symbols in the symbol table is 90.5096.....(=(2¹³)^1/2). Where three reels are used, the number of symbols in the symbol table is 20.1587.....(=(2¹³)^1/3). Where four reels are used, the number of symbols in the symbol table is 9.5136.....(=(2¹³)^1/4). Thus, perfect integers cannot be generated. For example, when three reels are used and 20 symbols in the symbol table is used, a total number of combinations of symbols is 8000 (=20³), and when 21 symbols are used, it is 9261 (=21³). thus, when 20 symbols are used, at least 192 (=8192-8000) random numbers are weighted by probability.
The above disadvantage is common to a mechanically driven slot machine in which the reels are mechanically rotated to move the symbol trains and a video type slot machine in which symbol trains are displayed on a CRT screen.
It is an object of the present invention to provide a slot machine wherein the number of random numbers in a random number table can be matched to the total number of combinations of symbols of the symbol trains.
Accordingly the invention provides a slot machine comprising X reels each reel comprising a plurality of symbols which form a symbol train having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, characterised in that said X reels include at least one reel having a total symbol number different to the total symbol numbers of the other reels and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together is equal to the total number of random numbers from which said random number is selected.
The slot machine may be one of the type which does not have mechanically driven reels; that is, a video type slot machine in which symbol trains are stored in a memory such as a ROM.
Accordingly, the invention also provides a slot machine comprising X symbol trains stored in a memory each of said symbol trains comprising a plurality of symbols and having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, characterised in that at least one of said X symbol trains stored in the memory has a total symbol number different to the total symbol numbers of the other symbol trains, and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together is equal to the total number of random numbers from which said random number is selected.
The invention also provides a slot machine comprising X reels, each reel comprising a plurality of symbols arranged on an outer periphery thereof to form a symbol train having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, said X reels comprising a first reel, a second reel and a plurality of other reels, characterised by said first reel having a larger number of a particular symbol which may form a winning combination of symbols than the other reels and said second reel having a smaller number of said particular symbol than the other reels, the probability of occurrence of a winning combination of said particular symbol from the symbol train of the first reel and the symbol train of the second reel being equal to the probability of occurrence of a winning combination of the same symbol from the symbol trains of the other reels on playing a game on said machine and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together being equal to the total number of random numbers from which said random number is selected.
The invention also provides a slot machine comprising X symbol trains stored in a memory, each of said symbol trains comprising a plurality of symbols and having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, said X symbol trains comprising a first symbol train, a second symbol train and a plurality of other symbol trains, characterised by said first symbol train having a larger number of a particular symbol which may form a winning combination of symbols than the other symbol trains and said second symbol train having a smaller number of said particular symbol than the other symbol trains, the probability of occurrence of a winning combination of said particular symbol from the first symbol train and the second symbol train being equal to the probability of occurrence of a winning combination of the same symbol from the other symbol trains and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together is equal to the total number of random numbers from which said random number is selected.
In order that the invention may be well understood, some embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings in which:

Fig. 1 shows a table listing the symbol trains arranged on outer peripheries of reels of a prior art slot machine;
Fig. 2 shows a table listing the symbol trains of a first embodiment of a slot machine in accordance with the present invention;
Fig. 3 is a front view of the slot machine of the first embodiment;
Fig. 4 is a functional block diagram of a circuit configuration of the slot machine of the first embodiment;
Fig. 5 is a perspective view showing reels which may be used in the slot machine of the first embodiment;
Fig. 6 shows a table listing the symbol trains of a second embodiment of a slot machine in accordance with the present invention,
Fig. 7 is a functional block diagram of a circuit configuration of the slot machine of the second embodiment; and
Figs. 8a and 8b show tables listing the probability of occurrence of some symbol combinations in the first and second embodiments of the slot machine.

A first embodiment of a slot machine in accordance with the present invention is explained with reference to Figs. 2 to 5.
Fig. 3 shows an external view of a three-reel type slot machine. In playing a game, a player inserts one to three coins into a coin port 1. Which of three winning lines X, Y and Z is valid in the game is determined in accordance with the number of coins inserted. When three coins are inserted, each line X, Y, Z is valid and a probability of winning is higher. Alternatively, if only one coin is inserted, line X is the only valid winning line. The number of coins inserted is digitally displayed by a coin count display 3. The coin count may be indicated by turning on an LED lamp which is related to number 1, 2 or 3. Then, the player depresses a start switch on a game switch unit 4 or pulls a start lever 2 so that respective stepping motors for rotating the first reel 5, second reel 6 and third reel 7 each having symbols arranged on the outer peripheries thereof to form symbol trains having a total symbol number are substantially simultaneously driven. As the first reel 5, second reel 6 and third reel 7 rotate, the player may observe the movement of the symbol trains through windows 8, 9 and 10 provided for the respective reels; though the player cannot identify the individual symbols.
The reels are driven through a microcomputer 32 and a motor driver 21. A stop position of each reel is determined under random number control by a random number generator 13. The stop position of the first reel 5 is determined when a coin (or coins) is inserted in the coinslot and the stop positions of the second reel 6 and the third reel 7 are determined when the player depresses the start switch on the game switch unit 4 or pulls the start lever 2. The random number generator 13 comprises a 13-bit register which can generate 8192 (=2¹³) random numbers. When the first reel 5, second reel 6 and third reel 7 stop rotating, the symbols which form the symbol combinations at the winning lines X, Y and Z are displayed. If there is a winning combination at any valid winning line, coins or tokens which are equal to the value of the win are paid out from a coin exit 11.
The number of coins inserted and the number of coins paid out are displayed on the display 3 and the game is over. If there is no winning combination displayed at any winning line, the player loses and the game is over.
If the player starts the game after he / she has depressed a bet switch on the game switch unit 4, no coins are paid out, instead the number of coins to be paid out is displayed on the display 3 as credit. The credited number is handled as if it were coins. That is, when the bet switch is depressed once, it is recognized as the insertion of one coin, and the credit number on the display 3 is decreased by one. If a max bet switch is depressed when the credit number is larger than a maximum coin count permitted for the game, it is recognized as the insertion of the maximum permitted number of coins for the game and the credit number on the display 3 is decreased by the maximum permitted number. When the player depresses a pay-out switch on the game switch unit 4, coins equal in number to the credit number are paid out from the coin exit 11.
Fig. 4 shows a functional block diagram of a circuit configuration of the three-reel type slot machine of Fig. 3. Before the game is started, the coins inserted in the coin port 1, are detected by a coin detector 12 one by one, and the count of detection pulses generated when the coins are detected is supplied to an MPU 16 as a coin count through an input port 14. The coin count supplied to the MPU 16 is stored in a RAM 19 by the MPU 16.
The MPU 16 converts the coin count to data for a display unit 28 and sends it to the display unit 28 so that the display 3 displays the coin count supplied to the MPU 16. The coin count stored in the RAM 19 provides information relating to the winning lines validated in the game for the MPU 16.
When the player a coin or coins and manipulates the start switch on the game switch unit 4 or the start lever 2, the MPU 16 reads that information through the input port 14 and activates the motor driver 21 to rotate the stepping motors 22, 23 and 24. The MPU 16 now supplies a drive pulse to the motor driver 16 by reference to a pulse generated by a pulse generator 18. The first reel 5, second reel 6 and third reel 7 are coupled to drive shafts of their respective stepping motors 22, 23 and 24 so that they rotate with same. A plurality of disproportion-type symbols having a different length in peripheral direction of the reel are arranged on the outer peripheries of each reel. Each symbol corresponds to one stop position. The symbol L having a relatively greater peripheral length bears a character such as "7B" or "5B", etc. and the symbol S having a relatively smaller peripheral length bears a blank (hereinafter referred as "BL"). Accordingly, as illustrated in Fig. 5, the symbol trains of the reels do not comprise a continuous arrangement of characters.
The numbers of pulses supplied to the stepping motor 22, 23 and 24 are stored in the RAM 19 from the MPU 16. Since the angle of rotation of the stepping motors 22, 23 and 24 changes with the number of pulses supplied thereto, the MPU 16 can uniquely determine the angular disposition of the respective shafts of the stepping motors 22, 23 and 24.
Projections 5a, 6a and 7a for producing reset signals are provided respectively on a portion of the circumference of the first reel 5, second reel 6 and third reel 7. The projections 5a, 6a and 7a are detected by respective photo- sensors 25, 26 and 27 in each revolution of the respective reels. The detection signals obtained are used to determine reference positions of the reels.
In this manner, the MPU 16 can determine the number of pulses to be supplied to the respective stepping motors in order to drive the reels to their required stop positions. The symbol position on the winning line when the first reel 5, second reel 6 and third reel 7 stop correspond to the numbers of pulses supplied to the stepping motors from the MPU 16.
In determining the outcome of a game, the winning lines validated by the number of coins inserted are taken into consideration. If a winning symbol combination appears on a valid winning line, the player wins the game and coins are paid out from the exit 11, or if the bet switch of the game switch 4 has been depressed, the number of coins to be paid out is displayed on the display 3 as credit. When coins are to be paid out, the MPU 16 supplies a hopper drive signal to a driver 29 through an output port 17 so that the hopper is driven and the coins are paid out. Each time a coin is paid out, a microswitch in the hopper is actuated to generate a pulse.
The pulse is sent to the MPU 16 through a driver 29 and an input port 14. Since the number of pulses sent to the MPU 16 corresponds to the number of coins paid out, the MPU 16 can determine the exact number of coins paid out.
When the number of pulses supplied reaches the number of coins to be paid out, the MPU 16 sends a hopper stop signal to the driver 29 through the output port 17 so that the hopper is stopped.
When the coins have been paid out, the number of coins paid out is displayed on the display 3. The number of coins inserted for the game is not erased until coins are newly inserted for the next game.
The symbol trains arranged on the outer peripheries of the first reel 5, second reel 6 and third reel 7 of the slot machine will now be explained with reference to Fig. 2. In the present embodiment, sixteen symbols are arranged on the outer periphery of each of the first reel 5 and second reel 6 and thirty-two symbols are arranged on the outer periphery of the third reel 7. Thus the total symbol number for the first and second reels is sixteen and the total symbol number for the third reel is thirty-two. In this case, one stop position is prepared for each symbol and the number of stop positions is equal to the number of symbols.
Each symbol train comprises four different symbols (7B, 5B, 1B, BL) of which symbols 7B, 5B and 1B are the symbols which may form a winning combination of symbols. The winning combinations are (1) 7B-7B-7B, (2) 5B-5B-5B, and (3) 1B-1B-1B. The symbol train on the first reel 5 includes the symbols 7B at a proportion of 4/16, the symbols 5B at a proportion of 4/16 and the symbols 1B at a proportion of 8/16. The symbol train on the second reel 6 includes the symbols 7B at a proportion of 2/16, the symbols 5B at a proportion of 2/16 and the symbols 1B at a proportion of 3/16. The symbol train on the third reel includes the symbols 7B at a proportion of 1/32, the symbols 5B at a proportion of 2/32 and the symbols 1B at a proportion of 3/32. Accordingly, when the first reel 5, second reel 6 and third reel 7 are rotated in playing a game, a probability of occurrence of 7B-7B-7B is 8/8192 (=4/4096), a probability of occurrence of 5B-5B-5B is 16/8192 (=8/4096) and a probability of occurrence of 1B-1B-1B is 72/8192(=36/4096). These probabilities are equal to the probability of occurrence of the same winning combinations in the symbol trains on the reels of the prior art slot machine (see Fig. 8). It is important to note that the slot machine comprises that a reel 7 having a total symbol number different to the total symbol number of the other reels 5, 6. As can be seen, the third reel 7 has thirty-two symbols whereas the first reel 5 and the second reel 6 each have only sixteen symbols. The total number of combinations of symbols is 8192 (=16×16×32) which is equal to the number of random numbers which may be generated by the random number generator 13, Accordingly, the combination of the symbols finally displayed on the winning line is not biased, and non-artificial natural game playing is attained.
In the case where a slot machine having a predetermined probability of occurrence of a particular winning combination of symbols is required, the degree of freedom is wide and it is easy to design. The following examples are given to illustrate this point.
The proportion of the number of a particular symbol which may form a winning combination of symbols at a winning line which is provided on each reel is arbitrarily determined. This proportion may be the same for some or all of the reels, even though the total number of symbols is different. In this case, the X reels may comprise a first reel of which the total symbol number is I and the number of a particular winning symbol is A and a second reel of which the total symbol number is J and the number of the same symbol is B, and A/I is equal to B/J. Alternatively the X reels may comprise a first reel of which the total symbol number is I, a second reel of which the total symbol number is J and a third reel of which the total symbol number is K where the number of a particular symbol which may form a winning combination of symbols provided on said first reel, said second reel and said third reel is respectively A, B and C, and A/I and B/J are equal to C/K.
Further, where X reels include a reel of which the total symbol number is I and the number of a particular winning symbol is A, another reel of which the total symbol number is J and the number of the same winning symbol is B and a further reel of which the total symbol number is K and the number of the same winning symbol is C, then (A/I)x(B/J) can be made equal to (C/K)² to provide the same probability of occurrence of a winning combination of the particular winning symbol as a slot machine with three reels which each have a total symbol number K and a number C of the particular symbol. This is demonstrated with reference to Fig. 2 in connection with winning symbol 5B, where A/I is 4/16 for the 1st reel, B/J is 2/32 for the 3rd reel and C/K is 2/16 for the 2nd reel.
Furthermore, in the case of a machine having four reels, comprising a reel having the above-described symbol proportion A/I and another reel having the above-described symbol proportion B/J, it is not necessary that the other two reels each have the previously described symbol proportion C/K to provide the same probability of occurrence of a winning combination of the particular winning symbol as a slot machine with four reels which each have the symbol proportion C/K. Instead, the other two reels may comprise a reel of which the total symbol number is H and the number of the particular winning symbol is D and a reel of which the total symbol number is M and the number of the particular winning symbol number is E where (D/H)×(E/M) can be made equal to (C/K)².
The above-described reel configuration may also be applied to a slot machine which determines the outcome of a game in accordance with a random number wherein the symbols are selected by referencing symbol tables (one provided for each reel) so that the game outcome may be displayed. In this case, the total symbol number of the symbol trains and their corresponding symbol tables may be different for each reel.
A second embodiment of the slot machine will now be described with reference to Figs. 6 and 7. A construction of a video-type slot machine of the present embodiment is first explained with reference to Fig. 7. Since an external view of such a slot machine is essentially the same as that of the first embodiment, an explanation thereof is omitted.
Fig. 7 shows a functional block diagram of a circuit configuration for a video-type machine corresponding to the mechanical three-reel type slot machine. n the video-type slot machine a CRT 37 is provided at the position corresponding to the position of the reels in Fig. 3. The CRT 37 is driven by a micro computer 38 and a CRT driver 39, and nine symbols in total are displayed in matrix form on the display screen.
Before the game is started, the number of coins inserted in the coin port is counted by a counter 40 with the data supplied via an input port 55. The number of valid winning lines on the display screen is determined by the number of coins inserted. The valid winning lines are referenced in determining the outcome of a game.
When a start button is depressed, a clock pulse is supplied from a pulse generator 41 to the CPU 43 and a microcomputer 38 is activated. The microcomputer 38 processes the game in accordance with a game program stored in a ROM 44. As the microcomputer 38 is activated, a CRT controller 45 is activated and character data of the symbols to be displayed on the CRT 37 from a character ROM 46 is accessed in an address sequence so that the symbols are displayed with scrolling effect. The ROM 44 stores, in addition to the game program, the contents of three symbol tables corresponding to the mechanical reels and a winning table.
The displayed symbol address data is held while it is sequentially updated in a RAM 47. After a predetermined time period, the scrolling of the first symbol train 49 vertically displayed on the CRT 37 is stopped by a stop signal generated by a random number generator 48 so that three symbols are specified (7B-7B-1B as illustrated). The random number generator 48 comprises a 12-bit shift register able to generate 4096 (=2¹²) random numbers. The scrolling of the second symbol train 52 and the third symbol train 53 is stopped in response to respective stop signals sequentially produced by delay signals 50 and 51 so that stop positions of the symbol trains are selected in accordance with the random number. In this manner, nine symbols in total are selected thereby determining the outcome of the game.
The RAM 47 stores the address data of the symbols displayed on the CRT 37. When the scrolling of the symbol trains 49, 52 and 53 has stopped so that the symbols at the winning lines are specified whether the combination of symbols displayed along a valid winning line is a winning combination or not may be checked. The address data stored in the winning table memory of the ROM 44 and the data stored in the RAM 47 are compared in performing the check.
Where a winning combination is formed at a winning line, the background of the symbols forming the winning combination may be changed or the color tone of the symbols may be reversed to that of regular display colors so that the winning combination is distinctively displayed. The CPU 43 has input port 55 and output port 56 connected thereto. The output port 56 supplies drive signal to a hopper 58 in response to a signal from the CPU 43. The hopper 58 pays out a predetermined number of coins corresponding to the type of winning in response to the signal from the output port 56. When the hopper 58 has paid out the predetermined number of coins, a normal symbol display mode is restored and the slot machine is reset to the initial state.
Referring to Fig. 6, the arrangement of the symbols which form the first symbol train 49, second symbol train 52 and third symbol train 53 of the three symbol tables (not shown) in the ROM 44 is explained. The three symbol table memories in the ROM 44 store eight symbols for the first symbol train 49, sixteen symbols for the second symbol train 52 and thirty-two symbols for the third symbol train 53. Thus in the present embodiment, the total symbol number of each symbol train is different to that of the other symbol trains. In this case, one stop position is prepared for each symbol and the number of symbols is equal to that of stop positions.
Each symbol train includes four different symbols (7B, 5B, 1B, BL), and the winning combinations are (1)7B-7B-7B, (2) 5B-5B-5B, and (3) 1B-1B-1B. The first symbol train 49 includes the symbols 7B at a proportion of 2/8, the symbols 5B at a proportion of 2/8, and the symbols 1B at a proportion of 4/8. The second symbol train 52 includes the symbols 7B at a proportion of 2/16, symbols 5B at a proportion of 2/16 and the symbols 1B at a proportion of 3/16. The third symbol train 53 includes the symbols 7B at a proportion of 1/32, symbols 5B at a proportion of 2/32 and the symbols 1B at a proportion of 3/32. Accordingly, when those symbol trains are simultaneously scrolled, a probability of occurrence of 7B-7B-7B is 4/4096, a probability of occurrence of 5B-5B-5B is 8/4096, and a probability of occurrence of 1B-1B-1B is 36/4096, which probabilities are equal to the probabilities in the symbol trains on the reels of the prior art slot machine (see Fig. 1).
It should be noted that the number of symbols in one of the three symbol trains is increased and the number of symbols in another symbol train is decreased relative to the sixteen symbol reels described in connection with the prior art slot machines, so that the final probability for the winning symbol combinations (for example, 7B-7B-7B) is not changed. To this end, the total symbol number of the second symbol train 52 is equal to sixteen (the same number as the reels of the prior art machine), the total symbol number of the first symbol train 49 is decreased from sixteen to eight, and the total symbol number of the third symbol train 53 is increased from sixteen to thirty-two so that the final probability does not change from that where the three sixteen symbol, symbol trains are used. The total number of symbol combinations is 4096 (=8×16×32) which is equal to the number of random numbers generated by the 12-bit register of the random generator 48. Accordingly, the combination of symbols displayed on a winning line is not biased, and non-artificial natural game playing is attained. As discussed above, there is a wide degree of freedom available and it is relatively easy to design a slot machine with predetermined probability of occurrence of a winning combination of symbols.
Figs. 8a and 8b show the probability of occurrence of some symbol combinations. Fig. 8A shows winning combinations, and Fig. 8B shows combinations of one-symbol losing and probabilities thereof. As seen from Fig. 8A, the number of a particular symbol can be controlled such that the probability of forming a winning combination of that symbol is not changed by changing the number of symbols of that particular type provided on the reels. In the slot machine of the present embodiment, however, the probabilities of combinations of one-symbol losing (for example, 7B-7B-5B) are high as seen from Fig. 8B.
It is to be understood that the number of reels, the total symbol number of the reels and the number of symbol trains whose total symbol numbers and/or numbers of particular symbols are increased or decreased is not limited to those described in conjunction with the above embodiments. For example, the symbol trains of the first embodiment (Fig. 2) and the symbol trains described in the examples given may be applied to the slot machine of the second embodiment and the symbol trains of the second embodiment (Fig. 6) may be applied to the slot machine of the first embodiment.
Furthermore, the number of symbol trains whose numbers of symbols are increased or decreased is not limited to two. For example, in a seven-reel slot machine, the number of a particular symbol which may form a winning combination on the first reel may be larger than the number of the same symbol on the fifth reel (or sixth or seventh reel) (hereinafter referred to as "reference number of symbols") and the number of the same symbol on the second reel may be smaller than the reference number, the number of the symbol on the third reel may be larger than the reference number, and the number of the symbol on the fourth reel may be smaller than the reference number. In this case, in playing a game the probability of occurrence of a winning combination (for example, 7B-7B) on the first and second reels is equal to the probability of occurrence of the same winning combination on the third and fourth reels and a probability of occurrence of a winning combination of the same symbol on the fifth and sixth reels (having the equal number of symbols).
Alternatively the numbers of the particular symbol on the first and second reels may be increased and the number of the same symbol on the third reel may be reduced. On playing a game, probability of the occurrence of a winning combination of the symbol (for example, 7B-7B-7B) on the first, second and third reels is equal to the probability of occurrence of the same winning combination on the fifth, sixth and seventh reels (each having an equal number of symbols).
It is to be understood that the total symbol number of the symbol trains is not limited to eight, sixteen or thirty-two.
Although the embodiments have been described in some detail it will be obvious to those skilled in the art upon reading and understanding the specification that the invention may be varied in many ways. It is intended to include such obvious variations as a part of the invention insofar as they come within the scope of the appended claims.

Claims

A slot machine comprising X reels (5, 6, 7) each reel comprising a plurality of symbols which form a symbol train having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, characterised in that said X reels include at least one reel (7) having a total symbol number different to the total symbol numbers of the other reels (5, 6) and the product obtained when the respective total symbol numbers of the symbol trains (5, 6, 7) are multiplied together is equal to the total number of random numbers from which said random number is selected.
A slot machine as claimed in claim 1, wherein said total number of random numbers is 2ⁿ derived from an n-bit binary number.
A slot machine as claimed in claim 1 or 2, wherein:
said X reels include a first reel of which the total symbol number is I and a second reel of which the total symbol number is J, where the number of a particular symbol provided on said first and second reels which may form a winning combination of symbols is respectively A and B, and A/I is equal to B/J.
A slot machine as claimed in claim 1 or 2, wherein:
said X reels comprise a first reel of which the total symbol number is I, a second reel of which the total symbol number is J and a third reel of which the total symbol number is K where the number of a particular symbol which may form a winning combination of symbols provided on said first reel, said second reel and said third reel is respectively A, B and C, and A/I and B/J are equal to C/K.
A slot machine as claimed in claim 1 or 2, wherein:
said X reels comprise a first reel of which the total symbol number is I, a second reel of which the total symbol number is J and a third reel of which the total symbol number is K where the number of a particular symbol which may form a winning combination of symbols provided on said first reel, said second reel and said third reel is respectively A, B and C, and (A/I)x(B/J) is equal to (C/K)².
A slot machine as claimed in claim 1 or 2, wherein:
said X reels comprise a first reel of which the total symbol number is I, a second reel of which the total symbol number is J, a third reel of which the total symbol number is K and a fourth reel of which the total symbol number is H, where the number of a particular symbol which may form a winning combination of symbols provided on said first reel, said second reel, said third reel and said fourth reel is respectively A, B, C and D, and (A/I)x(B/J) is equal to (C/K)x(D/H).
A slot machine comprising X symbol trains (49, 52, 53) stored in a memory (44) each of said symbol trains comprising a plurality of symbols and having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, characterised in that at least one (49, 52, 53) of said X symbol trains stored in the memory has a total symbol number different to the total symbol numbers of the other symbol trains, and the product obtained when the respective total symbol numbers of the symbol trains (49, 52, 53) are multiplied together is equal to the total number of random numbers from which said random number is selected.
A slot machine as claimed in claim 7, wherein said total number of random numbers is 2ⁿ derived from an n-bit binary number.
A slot machine as claimed in claim 7 or 8, wherein said X symbol trains comprise a first symbol train of which the total symbol number is I and a second symbol train of which the total symbol number is J, where the number of a particular symbol which may form a winning combination of symbols for said first symbol train and said second symbol train respectively is A and B, and A/I is equal to B/J.
A slot machine as claimed in claim 7 or 8, wherein said X symbol trains comprise a first symbol train of which the total symbol number is I, a second symbol train of which the total symbol number is J and a third symbol train of which the total symbol number is K where the number of a particular symbol which may form a winning combination of symbols for said first symbol train, said second symbol train and said third symbol train is respectively A, B and C, and A/I and B/J are equal to C/K.
A slot machine as claimed in claim 7 or 8, wherein said X symbol trains comprise a first symbol train of which the total symbol number is I, a second symbol train of which the total symbol number is J and a third symbol train of which the total symbol number is K where the number of a particular symbol which may form a winning combination of symbols for said first symbol train, said second symbol train and said third symbol train is respectively A, B and C, and (A/I)x(B/J) is equal to (C/K)².
A slot machine as claimed in claim 7 or 8, wherein said X symbol trains comprise a first symbol train of which the total symbol number is I, a second symbol train of which the total symbol number is J, a third symbol train of which the total symbol number is K and a fourth symbol train of which the total symbol number is H, where the number of a particular symbol which may form a winning combination of symbols for said first symbol train, said second symbol train, said third symbol train and said fourth symbol train is respectively A, B, C and D and (A/I)x(B/J) is equal to (C/K)x(D/H).
A slot machine comprising X reels, each reel comprising a plurality of symbols arranged on an outer periphery thereof to form a symbol train having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, said X reels comprising a first reel, a second reel and a plurality of other reels, characterised by said first reel having a larger number of a particular symbol which may form a winning combination of symbols than the other reels and said second reel having a smaller number of said particular symbol than the other reels, the probability of occurrence of a winning combination of said particular symbol from the symbol train of the first reel and the symbol train of the second reel being equal to the probability of occurrence of a winning combination of the same symbol from the symbol trains of the other reels on playing a game on said machine and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together being equal to the total number of random numbers from which said random number is selected.
A slot machine as claimed in claim 13 wherein, the total symbol number of said first reel is equal to that of said second reel.
A slot machine comprising X symbol trains stored in a memory, each of said symbol trains comprising a plurality of symbols and having a total symbol number, wherein an outcome of a game played on said machine is determined in accordance with a random number, said X symbol trains comprising a first symbol train, a second symbol train and a plurality of other symbol trains, characterised by said first symbol train having a larger number of a particular symbol which may form a winning combination of symbols than the other symbol trains and said second symbol train having a smaller number of said particular symbol than the other symbol trains, the probability of occurrence of a winning combination of said particular symbol from the first symbol train and the second symbol train being equal to the probability of occurrence of a winning combination of the same symbol from the other symbol trains and the product obtained when the respective total symbol numbers of the symbol trains are multiplied together is equal to the total number of random numbers from which said random number is selected.
A slot machine as claimed in claim 15, wherein the total symbol number of said first symbol train is equal to that of said second symbol train.