Patent Publication Number: US-2009233702-A1

Title: Gaming system, a method of gaming and a game controller

Description:
RELATED APPLICATIONS 
     This application claims priority to both Australian Provisional Patent Application Nos. 2008901143, having a filing date of Mar. 11, 2008, and 2008904501, having a filing date of Aug. 20, 2008, entitled “A Gaming System, A Method of Gaming and A Game Controller,” which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a gaming system, a method of gaming and a game controller. Current electronic gaming machines allow a player to place a wager or bet, in return for which a play of the game provided by the gaming machine is conducted. Many gaming machines implement a base game and a feature game which is triggered from the base game if one or more trigger conditions are met. Normally, the feature game has some different rules to the base game: for example, a sequence of free base games or a completely different game. A typical trigger condition is the occurrence of a particular symbol combination in the base game. In some games, a player must place an additional, ante bet to be eligible for the feature (or for a particular variant of the feature). 
     While such gaming machines provide users with enjoyment, a need exists for alternative gaming systems in order to maintain or increase player enjoyment. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first aspect, the invention provides a gaming system comprising: 
     a game play mechanism operable by a player to input an initiate base game instruction or to input an initiate feature game instruction; and 
     a game controller arranged to: 
     implement a base game in response to receipt of an initiate base game instruction and to implement a feature game triggerable from the base game when the feature game is triggered; 
     implement a feature game in response to receipt of an initiate feature game instruction; and 
     deduct different credit amounts in response to receipt of the initiate base game instruction and the initiate feature game instruction such that expected return to player is the same irrespective of the instruction. 
     In an embodiment, the game controller is arranged to deduct a different credit amount in response to the initiate feature game instruction by deducting a multiple of the credit amount deducted for an equivalent win entitlement in the base game. 
     In an embodiment, the game play mechanism is operable by the player to select from two or more different win entitlements. 
     In an embodiment, a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 Ft 
                 
                   Bt 
                   + 
                   F 
                 
               
             
             , 
           
         
       
     
     where
 
B=the expected base win per base game,
 
F=the expected feature win, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the feature game comprises a series of free games (n) and the feature game is retriggerable during the feature game and a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 nmt 
                 
                   t 
                   - 
                   n 
                   + 
                   nm 
                 
               
             
             , 
           
         
       
     
     where
 
m=a multiplier applied to wins during the feature, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the price (P) of the game in credits when the player enters the initiate feature game instruction is determined in accordance with the formula: 
         P =( RR/RTP )* NL*BL,    
     where RR is the ratio of the return from the feature game to the return from the base game; RTP is the average return to player; NL is the number of lines played; and BL is the bet per line. 
     In an embodiment, the game controller is implemented, at least in part, by a processor executing code stored in a memory of the gaming system. 
     In an embodiment, the game controller comprises a base game controller and a feature game controller for implementing the base and feature games respectively. 
     In an embodiment, the game controller comprises a credit controller arranged to determine the credit amounts to be deducted. 
     In a second aspect, the invention provides a game controller for a gaming system, the game controller arranged to: 
     implement a base game in response to receipt of an initiate base game instruction and to implement a feature game triggerable from the base game when the feature game is triggered; 
     implement a feature game in response to receipt of an initiate feature game instruction; and 
     deduct different credit amounts in response to receipt of the initiate base game instruction and the initiate feature game instruction such that expected return to player is the same irrespective of the instruction. 
     In an embodiment, the game controller is arranged to deduct a different credit amount in response to the initiate feature game instruction by deducting a multiple of the credit amount deducted for an equivalent win entitlement in the base game. 
     In an embodiment, a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 Ft 
                 
                   Bt 
                   + 
                   F 
                 
               
             
             , 
           
         
       
     
     where
 
B=the expected base win per base game,
 
F=the expected feature win, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the feature game comprises a series of free games (n) and the feature game is retriggerable during the feature game and a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 nmt 
                 
                   t 
                   - 
                   n 
                   + 
                   nm 
                 
               
             
             , 
           
         
       
     
     where
 
m=a multiplier applied to wins during the feature, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the price (P) of the game in credits when the player enters the initiate feature game instruction is determined in accordance with the formula: 
         P =( RR/RTP )* NL*BL,    
     where RR is the ratio of the return from the feature game to the return from the base game; RTP is the average return to player; NL is the number of lines played; and BL is the bet per line. 
     In an embodiment, the game controller is implemented, at least in part, by a processor executing code stored in a memory. 
     In an embodiment, the game controller comprises a base game controller and a feature game controller for implementing the base and feature games respectively. 
     In an embodiment, the game controller comprises a credit controller arranged to determine the credit amounts to be deducted. 
     In a third aspect, the invention provides a method of gaming comprising: 
     implementing a base game in response to receipt of an initiate base game instruction and to implement a feature game triggerable from the base game when the feature game is triggered; 
     implementing a feature game in response to receipt of an initiate feature game instruction; and 
     deducting different credit amounts in response to receipt of the initiate base game instruction and the initiate feature game instruction such that expected return to player is the same irrespective of the instruction. 
     In an embodiment, the method comprises deducting a different credit amount in response to the initiate feature game instruction by deducting a multiple of the credit amount deducted for an equivalent win entitlement in the base game. 
     In an embodiment, a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 Ft 
                 
                   Bt 
                   + 
                   F 
                 
               
             
             , 
           
         
       
     
     where
 
B=the expected base win per base game,
 
F=the expected feature win, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the feature game comprises a series of free games (n) and the feature game is retriggerable during the feature game and a multiplier (E) is derived in accordance with the equation 
     
       
         
           
             
               E 
               = 
               
                 nmt 
                 
                   t 
                   - 
                   n 
                   + 
                   nm 
                 
               
             
             , 
           
         
       
     
     where
 
m=a multiplier applied to wins during the feature, and
 
t=the trigger rate in number of games.
 
     In an embodiment, the price (P) of the game in credits when the player enters the initiate feature game instruction is determined in accordance with the formula: 
         P =( RR/RTP )* NL*BL,    
     where RR is the ratio of the return from the feature game to the return from the base game; RTP is the average return to player; NL is the number of lines played; and BL is the bet per line. 
     In a fourth aspect, the invention provides computer program code which when executed implements the above method. 
     In a fifth aspect, the invention provides a computer readable medium comprising the above program code. 
     In a sixth aspect, the invention provides a data signal comprising the above program code. 
     In a seventh aspect, the invention extends to transmitting the program code. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       An exemplary embodiment of the invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is a block diagram of the core components of a gaming system; 
         FIG. 2  is a perspective view of a stand alone gaming machine; 
         FIG. 3  is a block diagram of the functional components of a gaming machine; 
         FIG. 4  is a schematic diagram of the functional components of a memory; 
         FIG. 5  is a schematic diagram of a network gaming system; 
         FIG. 6  is a further block diagram of a gaming system; 
         FIG. 7  is an exemplary game play mechanism; and 
         FIG. 8  is a flow chart of an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, there is shown a gaming system having a game controller arranged to allow a player to purchase direct entry into a feature game. 
     General Construction of Gaming System 
     The gaming system can take a number of different forms. In a first form, a stand alone gaming machine is provided wherein all or most components required for implementing the game are present in a player operable gaming machine. 
     In a second form, a distributed architecture is provided wherein some of the components required for implementing the game are present in a player operable gaming machine and some of the components required for implementing the game are located remotely relative to the gaming machine. For example, a “thick client” architecture may be used wherein part of the game is executed on a player operable gaming machine and part of the game is executed remotely, such as by a gaming server; or a “thin client” architecture may be used wherein most of the game is executed remotely such as by a gaming server and a player operable gaming machine is used only to display audible and/or visible gaming information to the player and receive gaming inputs from the player. 
     However, it will be understood that other arrangements are envisaged. For example, an architecture may be provided wherein a gaming machine is networked to a gaming server and the respective functions of the gaming machine and the gaming server are selectively modifiable. For example, the gaming system may operate in stand alone gaming machine mode, “thick client” mode or “thin client” mode depending on the game being played, operating conditions, and so on. Other variations will be apparent to persons skilled in the art. 
     Irrespective of the form, the gaming system comprises several core components. At the broadest level, the core components are a player interface  50  and a game controller  60  as illustrated in  FIG. 1 . The player interface is arranged to enable manual interaction between a player and the gaming system and for this purpose includes the input/output components required for the player to enter instructions and play the game. 
     Components of the player interface may vary from embodiment to embodiment but will typically include a credit mechanism  52  to enable a player to input credits and receive payouts, one or more displays  54 , a game play mechanism  56  comprising one or more input devices that enable a player to input game play instructions (e.g. to place bets), and one or more speakers  58 . 
     The game controller  60  is in data communication with the player interface and typically includes a processor  62  that processes the game play instructions in accordance with game play rules and outputs game play outcomes to the display. Typically, the game play instructions are stored as program code in a memory  64  but can also be hardwired. Herein the term “processor” is used to refer generically to any device that can process game play instructions in accordance with game play rules and may include: a microprocessor, microcontroller, programmable logic device or other computational device, a general purpose computer (e.g. a PC) or a server. 
     A gaming system in the form of a stand alone gaming machine  10  is illustrated in  FIG. 2 . The gaming machine  10  includes a console  12  having a display  14  on which are displayed representations of a game  16  that can be played by a player. A mid-trim  20  of the gaming machine  10  houses a bank of buttons  22  for enabling a player to interact with the gaming machine, in particular during game play. The mid-trim  20  also houses a credit input mechanism  24  which in this example includes a coin input chute  24 A and a bill collector  24 B. Other credit input mechanisms may also be employed, for example, a card reader for reading a smart card, debit card or credit card. A player marketing module (not shown) having a reading device may also be provided for the purpose of reading a player tracking device, for example as part of a loyalty program. The player tracking device may be in the form of a card, flash drive or any other portable storage medium capable of being read by the reading device. 
     A top box  26  may carry artwork  28 , including for example pay tables and details of bonus awards and other information or images relating to the game. Further artwork and/or information may be provided on a front panel  29  of the console  12 . A coin tray  30  is mounted beneath the front panel  29  for dispensing cash payouts from the gaming machine  10 . 
     The display  14  shown in  FIG. 2  is in the form of a video display unit, particularly a cathode ray tube screen device. Alternatively, the display  14  may be a liquid crystal display, plasma screen, any other suitable video display unit, or the visible portion of an electromechanical device. The top box  26  may also include a display, for example a video display unit, which may be of the same type as the display  14 , or of a different type. 
       FIG. 3  shows a block diagram of operative components of a typical gaming machine which may be the same as or different to the gaming machine of  FIG. 2 . 
     The gaming machine  100  includes a game controller  101  having a processor  102 . Instructions and data to control operation of the processor  102  are stored in a memory  103 , which is in data communication with the processor  102 . Typically, the gaming machine  100  will include both volatile and non-volatile memory and more than one of each type of memory, with such memories being collectively represented by the memory  103 . 
     The gaming machine has hardware meters  104  for purposes including ensuring regulatory compliance and monitoring player credit, an input/output (I/O) interface  105  for communicating with peripheral devices of the gaming machine  100 . The input/output interface  105  and/or the peripheral devices may be intelligent devices with their own memory for storing associated instructions and data for use with the input/output interface or the peripheral devices. A random number generator module  113  generates random numbers for use by the processor  102 . Persons skilled in the art will appreciate that the reference to random numbers includes pseudo-random numbers. 
     In the example shown in  FIG. 3 , a player interface  120  includes peripheral devices that communicate with the game controller  101  comprise one or more displays  106 , a touch screen and/or buttons  107 , a card and/or ticket reader  108 , a printer  109 , a bill acceptor and/or coin input mechanism  110  and a coin output mechanism  111 . Additional hardware may be included as part of the gaming machine  100 , or hardware may be omitted as required for the specific implementation. For example, while buttons or touch screens are typically used in gaming machines to allow a player to place a wager and initiate a play of a game any input device that enables the player to input game play instructions may be used. For example, in some gaming machines a mechanical handle is uses to initiate a play of the game. 
     In addition, the gaming machine  100  may include a communications interface, for example a network card  112 . The network card may, for example, send status information, accounting information or other information to a central controller, server or database and receive data or commands from the central controller, server or database. 
       FIG. 4  shows a block diagram of the main components of an exemplary memory  103 . The memory  103  includes RAM  103 A, EPROM  103 B and a mass storage device  103 C. The RAM  103 A typically temporarily holds program files for execution by the processor  102  and related data. The EPROM  103 B may be a boot ROM device and/or may contain some system or game related code. The mass storage device  103 C is typically used to store game programs, the integrity of which may be verified and/or authenticated by the processor  102  using protected code from the EPROM  103 B or elsewhere. It is also possible for the operative components of the gaming machine  100  to be distributed, for example input/output devices  106 , 107 , 108 , 109 , 110 , 111  to be provided remotely from the game controller  101 . 
       FIG. 5  shows a gaming system  200  in accordance with an alternative embodiment. The gaming system  200  includes a network  201 , which for example may be an Ethernet network. Gaming machines  202 , shown arranged in three banks  203  of two gaming machines  202  in  FIG. 5 , are connected to the network  201 . The gaming machines  202  provide a player operable interface and may be the same as the gaming machines  10 , 100  shown in  FIGS. 2 and 3 , or may have simplified functionality depending on the requirements for implementing game play. While banks  203  of two gaming machines are illustrated in  FIG. 5 , banks of one, three or more gaming machines are also envisaged. 
     One or more displays  204  may also be connected to the network  201 . For example, the displays  204  may be associated with one or more banks  203  of gaming machines. The displays  204  may be used to display representations associated with game play on the gaming machines  202 , and/or used to display other representations, for example promotional or informational material. 
     In a thick client embodiment, game server  205  implements part of the game played by a player using a gaming machine  202  and the gaming machine  202  implements part of the game. With this embodiment, as both the game server and the gaming device implement part of the game, they collectively provide a game controller. A database management server  206  may manage storage of game programs and associated data for downloading or access by the gaming devices  202  in a database  206 A. Typically, if the gaming system enables players to participate in a Jackpot game, a Jackpot server  207  will be provided to perform accounting functions for the Jackpot game. A loyalty program server  212  may also be provided. 
     In a thin client embodiment, game server  205  implements most or all of the game played by a player using a gaming machine  202  and the gaming machine  202  essentially provides only the player interface. With this embodiment, the game server  205  provides the game controller. The gaming machine will receive player instructions, pass these to the game server which will process them and return game play outcomes to the gaming machine for display. In a thin client embodiment, the gaming machines could be computer terminals, e.g. PCs running software that provides a player interface operable using standard computer input and output components. Other client/server configurations are possible, and further details of a client/server architecture can be found in WO 2006/052213 and PCT/SE2006/000559, the disclosures of which are incorporated herein by reference. 
     Servers are also typically provided to assist in the administration of the gaming network  200 , including for example a gaming floor management server  208 , and a licensing server  209  to monitor the use of licenses relating to particular games. An administrator terminal  210  is provided to allow an administrator to run the network  201  and the devices connected to the network. 
     The gaming system  200  may communicate with other gaming systems, other local networks, for example a corporate network, and/or a wide area network such as the Internet, for example through a firewall  211 . 
     Persons skilled in the art will appreciate that in accordance with known techniques, functionality at the server side of the network may be distributed over a plurality of different computers. For example, elements may be run as a single “engine” on one server or a separate server may be provided. For example, the game server  205  could run a random generator engine. Alternatively, a separate random number generator server could be provided. Further, persons skilled in the art will appreciate that a plurality of game servers could be provided to run different games or a single game server may run a plurality of different games as required by the terminals. 
     Further Detail of Gaming System 
     Referring to  FIG. 6 , in the embodiment, the player operates game play mechanism  56  to specify their win entitlement and whether they want to play the base game or purchase direct entry into a feature game triggerable from the base game at a trigger rate (t). Game play mechanism  56  provides a series of buttons (either physical buttons or depictions of buttons on a touch screen) that allows the player to make the selections. The selections include a first class of selection that specifies the player&#39;s win entitlement and a second class that indicates whether that win entitlement will be evaluated in a base game or a feature game and hence whether a initiate base game or initiate feature game instruction will be communicated from the game play mechanism  56  to the game controller  60 . Parts of the player&#39;s selection may be combined in a single button. For example, a player&#39;s indication that they want to play five lines may also provide an initiate base game instruction to the game controller Depending on the embodiment, not all win entitlements available for entering the base game may be available when entering the feature game. For example, direct entries to the feature game may be restricted to the player choosing to play all win lines. 
     Persons skilled in the art will appreciate that a player&#39;s win entitlement will vary from game to game and may or may not be dependent on player selections. In most spinning reel games, it is typical for the player&#39;s entitlement to be affected by the amount they wager and selections they make (i.e. the nature of the wager). For example, a player&#39;s win entitlement may be based on how many lines they will play in each game—i.e. a minimum of one line up to the maximum number of lines allowed by the game (noting that not all permutations of win lines may be available for selection, for example, 1, 5, 10 and 20 lines may be offered). Such win lines are typically formed by a combination of displayed symbol positions, one from each reel, the symbol positions being located relative to one another such that they form a line. 
     In many games, the player&#39;s win entitlement is not strictly limited to the lines they have selected, for example, “scatter” pays are awarded independently of a players selection of pay lines and are an inherent part of the win entitlement. 
     Persons skilled in the art, will appreciate that in other embodiments, the player may obtain a win entitlement by selecting a number of reels to play. 
     Such games are marketed under the trade name “Reel Power” by Aristocrat Leisure Industries Pty Ltd. The selection of the reel means that each displayed symbol of the reel can be substituted for a symbol at one or more designated display positions. In other words, all displayed symbol positions of a selected reel can be used to form symbol combinations with designated, displayed symbol positions of other reels. 
     In other embodiments a player win entitlement may be affected by purchasing access to particular pay tables—e.g. a first bet amount entitles the player to wins including cherries and a second amount entitles them to wins including plums. 
       FIG. 7  shows a game play mechanism  56  of an embodiment where the player selects win lines. Six buttons  711 , 712 , 721 , 722 , 731 , 732  are available to the player A player has a choice of whether they will bet  1  credit per line  711  or 5 credits per line. The player completes the specification of their win entitlement by selecting one of buttons  721 , 722 , 731 , 732  which correspond respectively to playing 1 line of the base game, playing 9 lines of the base game, playing 1 line of the feature game and playing 9 lines of the feature game. Each button  721 , 722 , 731 , 732  also provides either an initiate base game play instruction  721 , 722  or an initiate feature game instruction  731 , 732  to game controller  60 . In some embodiments, the options for direct entry into the feature game may be limited, for example only available if the player is playing the maximum base play option, such as the maximum number lines. 
     Persons skilled in the art will appreciate that typically feature games are triggered occasional or rarely and with a prize offering significant return to the player. Many features require no additional bet. Accordingly, in order that the gaming system provide the same return to players who enter the base game as enter the feature game. This is achieved by deducting credits for direct entry into the feature game at a multiplier of the amount of credits required for an equivalent base game based on the relative return to player provided by the feature game as described in further detail in the accompanying examples. Factors used in determining the multiplier, or ante-bet for entering the feature game directly include the rate at which the feature triggers, whether a multiplier is applied in the feature and whether the feature can be retriggered. 
     When game controller  60  receives an initiate play instruction, credit controller  624  ensures that the correct amount of credits will be deducted in dependence on whether the game is to be a base or feature game. Usually, the credits are not deducted from the credit enter specified by meter data  643  until the play has been completed and the win(s) from the player are known so that a net adjustment of the credit meter may be made. 
     Game controller then initiates either base game controller  622  of feature game controller  623  which implement the base or feature games respectively based on base game data  642  or feature game data  641 . Both controllers  622 , 623  employ random number generator  621  to generate game outcomes which are evaluated to determined whether an award of credits is to be made. If the base game triggers a feature game, base game controller  622  passes control to feature game controller  623  to carry out the triggered feature game before returning control to base game controller  622 . 
     The method provided by the embodiment is summarised in  FIG. 8 . Initially the game controller  60  waits  810  for an initiate play instruction. It determines  820  whether the initiate play instruction is a base game instruction. If it is, a base game is played  840  and it is determined  850  whether a feature game is triggered. If a feature game is triggered, the method involves playing the feature  860  before returning to a waiting  810  state. If a base game is not selected at  820 , then the instruction will be a feature game selection  830  and the feature game is played  860  via direct entry. 
     Persons skilled in the art will also appreciate that the method of the embodiment could be embodied in program code. The program code could be supplied in a number of ways, for example on a computer readable medium, such as a disc or a memory (for example, that could replace part of memory  103 ) or as a data signal (for example, by downloading it from a server). 
     The game can be a spinning reel game, a poker game, a pin and ball game, a keno or bingo game, dice game or card game or any other game known in the art. Further the base and feature games can be different. 
     In the above examples, the player can at any time purchase the feature game. If the feature game is already in play, then the commencement of the purchased feature game commences at the conclusion of the purchased feature game. In an alternative, embodiment one or more rules specify, when the feature game is eligible to be purchased, for example, the initiate play instruction may need to be in respect of a bet amount per line of a certain value. 
     Example 1 
     In this example a feature with average pay of 36 times the total bet may be awarded on average once every 100 games thus contributing an average of 36% return to player. In between features the player may play a 54% base with a total bet per game of 25¢. The total return to the player is 54%+36%=90%. Thus, on average between each feature, 
     the player spends 100×25¢=$25.00
 
the player wins 100×54%×25¢=$13.50
 
the player loses 100×(1−54%)×25¢=$11.50
 
     The feature of 36 times the bet is a reward of 
     feature pay 36×25¢=$9.00 
     Hence the $11.50 lost in the base game buys back a $9.00 feature, on average. The net loss of $25 bet−$13.40 base win−$9.00 feature win=$2.50 from $25 bet reflects the 90% return to the player. 
     Instead of playing 100 base games to get the feature, the player may be offered the chance to buy the feature for an appropriate price. In this case a feature of 36 times the normal bet may be offered to the player for 40 times the normal bet, the return is unchanged as 36/40=90%. A 25 line game on a 1 ¢ denomination with a feature of 36× total bet can offer a feature for a cost of 40×25¢=$10.00. That is, the ante bet multiplier, E=(Feature RTP % *100)/RTP % 
     A general expression for the ante bet E as a multiplier of the normal bet for this bought feature is as follows: 
     expected base win (per base game in $) B
 
expected feature win (per feature in $) F
 
trigger rate (in number of games) t
 
     
       
         
           
             E 
             = 
             
               1 
               
                 
                   B 
                   F 
                 
                 + 
                 
                   1 
                   t 
                 
               
             
           
         
       
     
     Note that the feature win will be in addition to any base win in the game from which it is triggered, so that for each t games there will be t base games +1 feature game. The above expression can be re-written as: 
     
       
         
           
             E 
             = 
             
               Ft 
               
                 Bt 
                 + 
                 F 
               
             
           
         
       
     
     The numerator represents the return that can be expected over the number of trigger games if each game if it is played as a feature game, whereas the denominator represents the return that would normally be expected from that number of games and hence, E represents the ration of increased return. 
     Persons skilled in the art will appreciate that the above equations can be applied to both units of currency or units of credits. 
     Example 2 
     Free Games with Multiplier 
     In games, where there the feature is a series n of free base games. F=nB and if a multiplier m is applied during the free games, then F=nMB. So that 
     
       
         
           
             E 
             = 
             
               nmt 
               
                 t 
                 + 
                 nm 
               
             
           
         
       
     
     Example 3 
     Retriggerable Feature 
     In some games, the feature is retriggerable, if the trigger occurs during the free games, a retriggerable free game feature with 
     free games n
 
multiplier m
 
trigger rate t
 
such as Queen Of The Nile (manufactured by Aristocrat) can be bought with an appropriate ante bet E which will immediately commence play of the n free games retriggerable with probability 1/t and with all wins multiplied by multiplier m.
 
     
       
         
           
             E 
             = 
             
               nmt 
               
                 t 
                 - 
                 n 
                 + 
                 nm 
               
             
           
         
       
     
     Persons skilled in the art will appreciate that, it is possible to have multiple features such that the feature F 1 , bought with bet E 1  may be part of the underlying game or may not. Further features F 2 , F 3 , F 4 , . . . may be created such that F 2  occasionally triggered with ante bet E 1  upon buying F 1 , but F 2  may be bought by a further ante bet E 2  etc. 
     Example 4 
     The feature game is usually triggered by the occurrence of an event. The event can be a game event (e.g. a certain set of symbols on a pay line), a machine event (e.g. a random number is selected by the machine), a system event or a player tracking system event. 
     The feature game usually contributes x % to the total return to player. The feature game has a probability of occurrence of p (where 0≦p≦1) 
     In a spinning reel game with a free game feature, the free game feature normally commences when 3 scattered cats appear anywhere in the window. The free game feature consists of 10 free games playing the lines and bet per line which were in play when the feature was triggered. The feature game returns on average 15 times the bet which was in play when the feature was triggered. The total return to player is 90%. 
     The player is offered the option at any time that the feature game is not already in play, to purchase the feature game feature. 
     The price of the feature game is calculated as 15/0.9=17 credits (with rounding to the nearest credit) multiplied by the number of lines to be purchased and multiplied by the bet per line—i.e. P=(RR/RTP)*NL*BL, where: P is the price in credits; RM is the ratio of the return from the feature game to the return from the base game; RTP is the average return to player; NL is the number of lines played; and BL is the bet per line. 
     The player chooses to purchase 20 lines at 2 credits per line, so the cost is 17*2*20=680 credits. The player presses the purchase “feature game” button and the credit meter decrements by 680 credits. The player is advised that a feature game is now in progress and the feature game commences. At the conclusion of the purchased feature game, we expect the player to receive 15*2*20=600 credits. This gives an expected player return of 88.2%. 
     Example 5 
     A spinning reel game is provided with 2 types of feature games. Feature game A is a hold and re-spin game, feature game B is as per the feature game in example 4 and can be purchased in the same manner. In this example, either feature game can be purchased at any time provided a feature game is not already in play. The total game has a return to player of 90%. 
     Feature game A is a game in which the feature usually commences whenever a pair of “wild” symbols occurs on the first 2 reels. The first 2 reels are held and the player pays the originating bet and the remaining reels are spun. Any win is paid and the player pays the originating bet again, the first 2 reels are held and the remaining reels are spun. At the conclusion of the 2 re-spins, the game returns to the usual game. Feature A is expected to return 10 credits for each credit bet at the time the feature commences. 
     In this game, the player is playing the game and chooses to purchase feature game A. The price for feature game A is 10/0.9=11 credits times the total bet (with rounding to the nearest credit). 
     The player selects to purchase feature A with 10 lines played at 5 credits per line. The credit meter is decremented by 550 credits and the player is advised that the feature re-spin game is now in play. If necessary, the screen and reel strips change and the player sees the reels spin and a pair of “wild” symbols land on the first 2 reels. Any prize is paid. The player then bets 550 credits again and the first 2 reels are held and the remaining reels are spun. Any prizes are paid. The player then bets 550 credits and the first 2 reels are held and the remaining reels are spun. Any prizes are paid. 
     It is expected that 10*5*10=500 credits will be paid on each of the 3 spins. The total return to player is 500+500+500 for an investment of 3*550. This is a return to player of 90.9%. 
     It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. In particular, features of the above embodiments and examples can be employed to form further embodiments. 
     It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art. 
     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.