Slot machine

Historically, all slot machines used revolving mechanical reels to display and determine results. Although the original slot machine used five reels, simpler, and therefore more reliable, three reel machines quickly became the standard.

A problem with three reel machines is that the number of combinations is only cubic – the original slot machine with three physical reels and 10 symbols on each reel had only 10³ = 1,000 possible combinations. This limited the manufacturer's ability to offer large jackpots since even the rarest event had a likelihood of 0.1%. The maximum theoretical payout, assuming 100% return to player would be 1000 times the bet, but that would leave no room for other pays, making the machine very high risk, and also quite boring.

Although the number of symbols eventually increased to about 22, allowing 10,648 combinations,[20] this still limited jackpot sizes as well as the number of possible outcomes.

In the 1980s, however, slot machine manufacturers incorporated electronics into their products and programmed them to weight particular symbols. Thus the odds of losing symbols appearing on the payline became disproportionate to their actual frequency on the physical reel. A symbol would only appear once on the reel displayed to the player, but could, in fact, occupy several stops on the multiple reel.

In 1984 Inge Telnaes received a patent for a device titled, "Electronic Gaming Device Utilizing a Random Number Generator for Selecting the Reel Stop Positions" (US Patent 4448419),[21] which states: "It is important to make a machine that is perceived to present greater chances of payoff than it actually has within the legal limitations that games of chance must operate." [22] The patent was later bought by International Game Technology and has since expired.

A virtual reel that has 256 virtual stops per reel would allow up to 256³ = 16,777,216 final positions. The manufacturer could choose to offer a $1 million dollar jackpot on a $1 bet, confident that it will only happen, over the long term, once every 16.8 million plays.

With microprocessors now ubiquitous, the computers inside modern slot machines allow manufacturers to assign a different probability to every symbol on every reel. To the player it might appear that a winning symbol was "so close", whereas in fact the probability is much lower.

In the 1980s in the U.K., machines embodying microprocessors became common. These used a number of features to ensure the payout was controlled within the limits of the gambling legislation. As a coin was inserted into the machine, it could go either directly into the cashbox for the benefit of the owner or into a channel that formed the payout reservoir, with the microprocessor monitoring the number of coins in this channel. The drums themselves were driven by stepper motors, controlled by the processor and with proximity sensors monitoring the position of the drums. A "look-up table" within the software allows the processor to know what symbols were being displayed on the drums to the gambler. This allowed the system to control the level of payout by stopping the drums at positions it had determined. If the payout channel had filled up, the payout became more generous; if nearly empty, the payout became less so (thus giving good control of the odds).

Video slot machines do not use mechanical reels, instead of using graphical reels on a computerized display. As there are no mechanical constraints on the design of video slot machines, games often use at least five reels, and may also use non-standard layouts. This greatly expands the number of possibilities: a machine can have 50 or more symbols on a reel, giving odds as high as 300 million to 1 against – enough for even the largest jackpot. As there are so many combinations possible with five reels, manufacturers do not need to weight the payout symbols (although some may still do so). Instead, higher paying symbols will typically appear only once or twice on each reel, while more common symbols earning a more frequent payout will appear many times. Video slot machines usually make more extensive use of multimedia, and can feature more elaborate minigames as bonuses. Modern cabinets typically use flat-panel displays, but cabinets using larger curved screens (which can provide a more immersive experience for the player) are not uncommon.[23]

Video slot machines typically encourage the player to play multiple "lines": rather than simply taking the middle of the three symbols displayed on each reel, a line could go from top left to the bottom right or any other pattern specified by the manufacturer. As each symbol is equally likely, there is no difficulty for the manufacturer in allowing the player to take as many of the possible lines on offer as desire – the long-term return to the player will be the same. The difference for the player is that the more lines they play, the more likely they are to get paid on a given spin (because they are betting more).

To avoid seeming as if the player's money is simply ebbing away (whereas a payout of 100 credits on a single-line machine would be 100 bets and the player would feel they had made a substantial win, on a 20-line machine, it would only be five bets and not seem as significant), manufacturers commonly offer bonus games, which can return many times their bet. The player is encouraged to keep playing to reach the bonus: even if he is losing, the bonus game could allow then to win back their losses.

All modern machines are designed using pseudorandom number generators ("PRNGs"), which are constantly generating a sequence of simulated random numbers, at a rate of hundreds or perhaps thousands per second. As soon as the "Play" button is pressed, the most recent random number is used to determine the result. This means that the result varies depending on exactly when the game is played. A fraction of a second earlier or later and the result would be different.

It is important that the machine contains a high-quality RNG implementation. Because all PRNGs must eventually repeat their number sequence[24] and, if the period is short or the PRNG is otherwise flawed, an advanced player may be able to "predict" the next result. Having access to the PRNG code and seed values, Ronald Dale Harris, a former slot machine programmer, discovered equations for specific gambling games like Keno that allowed him to predict what the next set of selected numbers would be based on the previous games played.

Most machines are designed to defeat this by generating numbers even when the machine is not being played so the player cannot tell where in the sequence they are, even if they know how the machine was programmed.

Slot machines are typically programmed to pay out as winnings 0% to 99% of the money that is wagered by players. This is known as the "theoretical payout percentage" or RTP, "return to player". The minimum theoretical payout percentage varies among jurisdictions and is typically established by law or regulation. For example, the minimum payout in Nevada is 75%, in New Jersey 83%, and in Mississippi 80%. The winning patterns on slot machines – the amounts they pay and the frequencies of those payouts – are carefully selected to yield a certain fraction of the money paid to the "house" (the operator of the slot machine) while returning the rest to the players during play. Suppose that a certain slot machine costs $1 per spin and has a return to player (RTP) of 95%. It can be calculated that, over a sufficiently long period such as 1,000,000 spins, the machine will return an average of $950,000 to its players, who have inserted $1,000,000 during that time. In this (simplified) example, the slot machine is said to pay out 95%. The operator keeps the remaining $50,000. Within some EGM development organizations this concept is referred to simply as "par". "Par" also manifests itself to gamblers as promotional techniques: "Our 'Loose Slots' have a 93% payback! Play now!"

A slot machine's theoretical payout percentage is set at the factory when the software is written. Changing the payout percentage after a slot machine has been placed on the gaming floor requires a physical swap of the software or firmware, which is usually stored on an EPROM but may be loaded onto non-volatile random access memory (NVRAM) or even stored on CD-ROM or DVD, depending on the capabilities of the machine and the applicable regulations. Based on current technology, this is a time-consuming process and as such is done infrequently. In certain jurisdictions, such as New Jersey, the EPROM has a tamper-evident seal and can only be changed in the presence of Gaming Control Board officials. Other jurisdictions, including Nevada, randomly audit slot machines to ensure that they contain only approved software.

Historically, many casinos, both online and offline, have been unwilling to publish individual game RTP figures, making it impossible for the player to know whether they are playing a "loose" or a "tight" game. Since the turn of the century some information regarding these figures has started to come into the public domain either through various casinos releasing them—primarily this applies to online casinos—or through studies by independent gambling authorities.

The return to player is not the only statistic that is of interest. The probabilities of every payout on the pay table is also critical. For example, consider a hypothetical slot machine with a dozen different values on the pay table. However, the probabilities of getting all the payouts are zero except the largest one. If the payout is 4,000 times the input amount, and it happens every 4,000 times on average, the return to player is exactly 100%, but the game would be dull to play. Also, most people would not win anything, and having entries on the paytable that have a return of zero would be deceptive. As these individual probabilities are closely guarded secrets, it is possible that the advertised machines with high return to player simply increase the probabilities of these jackpots. The casino could legally place machines of a similar style payout and advertise that some machines have 100% return to player. The added advantage is that these large jackpots increase the excitement of the other players.

The table of probabilities for a specific machine is called the Probability and Accounting Report or PAR sheet, also PARS commonly understood as Paytable and Reel Strips. Mathematician Michael Shackleford revealed the PARS for one commercial slot machine, an original International Gaming Technology Red White and Blue machine. This game, in its original form, is obsolete, so these specific probabilities do not apply. He only published the odds after a fan of his sent him some information provided on a slot machine that was posted on a machine in the Netherlands. The psychology of the machine design is quickly revealed. There are 13 possible payouts ranging from 1:1 to 2,400:1. The 1:1 payout comes every 8 plays. The 5:1 payout comes every 33 plays, whereas the 2:1 payout comes every 600 plays. Most players assume the likelihood increases proportionate to the payout. The one mid-size payout that is designed to give the player a thrill is the 80:1 payout. It is programmed to occur an average of once every 219 plays. The 80:1 payout is high enough to create excitement, but not high enough that it makes it likely that the player will take their winnings and abandon the game. More than likely the player began the game with at least 80 times his bet (for instance there are 80 quarters in $20). In contrast the 150:1 payout occurs only on average of once every 6,241 plays. The highest payout of 2,400:1 occurs only on average of once every 64³ = 262,144 plays since the machine has 64 virtual stops. The player who continues to feed the machine is likely to have several mid-size payouts, but unlikely to have a large payout. He quits after he is bored or has exhausted his bankroll.

Despite their confidentiality, occasionally a PAR sheet is posted on a website. They have limited value to the player, because usually a machine will have 8 to 12 different possible programs with varying payouts. In addition, slight variations of each machine (e.g., with double jackpots or five times play) are always being developed. The casino operator can choose which EPROM chip to install in any particular machine to select the payout desired. The result is that there is not really such a thing as a high payback type of machine, since every machine potentially has multiple settings. From October 2001 to February 2002, columnist Michael Shackleford obtained PAR sheets for five different nickel machines; four IGT games Austin Powers, Fortune Cookie, Leopard Spots and Wheel of Fortune and one game manufactured by WMS; Reel 'em In. Without revealing the proprietary information, he developed a program that would allow him to determine with usually less than a dozen plays on each machine which EPROM chip was installed. Then he did a survey of over 400 machines in 70 different casinos in Las Vegas. He averaged the data, and assigned an average payback percentage to the machines in each casino. The resultant list was widely publicized for marketing purposes (especially by the Palms casino which had the top ranking).

One reason that the slot machine is so profitable to a casino is that the player must play the high house edge and high payout wagers along with the low house edge and low payout wagers. In a more traditional wagering game like craps, the player knows that certain wagers have almost a 50/50 chance of winning or losing, but they only pay a limited multiple of the original bet (usually no higher than three times). Other bets have a higher house edge, but the player is rewarded with a bigger win (up to thirty times in craps). The player can choose what kind of wager he wants to make. A slot machine does not afford such an opportunity. Theoretically, the operator could make these probabilities available, or allow the player to choose which one so that the player is free to make a choice. However, no operator has ever enacted this strategy. Different machines have different maximum payouts, but without knowing the odds of getting the jackpot, there is no rational way to differentiate.

In many markets where central monitoring and control systems are used to link machines for auditing and security purposes, usually in wide area networks of multiple venues and thousands of machines, player return must usually be changed from a central computer rather than at each machine. A range of percentages is set in the game software and selected remotely.

In 2006, the Nevada Gaming Commission began working with Las Vegas casinos on technology that would allow the casino's management to change the game, the odds, and the payouts remotely. The change cannot be done instantaneously, but only after the selected machine has been idle for at least four minutes. After the change is made, the machine must be locked to new players for four minutes and display an on-screen message informing potential players that a change is being made.[25]

Some varieties of slot machines can be linked together in a setup sometimes known as a "community" game. The most basic form of this setup involves progressive jackpots that are shared between the bank of machines, but may include multiplayer bonuses and other features.[26]

In some cases multiple machines are linked across multiple casinos. In these cases, the machines may be owned by the manufacturer, who is responsible for paying the jackpot. The casinos lease the machines rather than owning them outright. Casinos in New Jersey, Nevada, and South Dakota now offer multi-state progressive jackpots, which now offer bigger jackpot pools.[27][28]

Mechanical slot machines and their coin acceptors were sometimes susceptible to cheating devices and other scams. One historical example involved spinning a coin with a short length of plastic wire. The weight and size of the coin would be accepted by the machine and credits would be granted. However, the spin created by the plastic wire would cause the coin to exit through the reject chute into the payout tray. This particular scam has become obsolete due to improvements in newer slot machines. Another obsolete method of defeating slot machines was to use a light source to confuse the optical sensor used to count coins during payout.[29]

Modern slot machines are controlled by EPROM computer chips and, in large casinos, coin acceptors have become obsolete in favor of bill acceptors. These machines and their bill acceptors are designed with advanced anti-cheating and anti-counterfeiting measures and are difficult to defraud. Early computerized slot machines were sometimes defrauded through the use of cheating devices, such as the "slider", "monkey paw", "lightwand" and "the tongue". Many of these old cheating devices were made by the late Tommy Glenn Carmichael, a slot machine fraudster who reportedly stole over $5 million.[30] In the modern day, computerized slot machines are fully deterministic and thus outcomes can be sometimes successfully predicted.[31]

Malfunctioning electronic slot machines are capable of indicating jackpot winnings far in excess of those advertised.[32] Two such cases occurred in casinos in Colorado in 2010, where software errors led to indicated jackpots of $11 million and $42 million. Analysis of machine records by the state Gaming Commission revealed faults, with the true jackpot being substantially smaller.[33] State gaming laws do not require a casino to honour payouts.

In the United States, the public and private availability of slot machines is highly regulated by state governments. Many states have established gaming control boards to regulate the possession and use of slot machines and other form of gaming.

Nevada is the only state that has no significant restrictions against slot machines both for public and private use. In New Jersey, slot machines are only allowed in hotel casinos operated in Atlantic City. Several states (Indiana, Louisiana and Missouri) allow slot machines (as well as any casino-style gambling) only on licensed riverboats or permanently anchored barges. Since Hurricane Katrina, Mississippi has removed the requirement that casinos on the Gulf Coast operate on barges and now allows them on land along the shoreline. Delaware allows slot machines at three horse tracks; they are regulated by the state lottery commission. In Wisconsin, bars and taverns are allowed to have up to five machines. These machines usually allow a player to either take a payout, or gamble it on a double-or-nothing "side game".

The territory of Puerto Rico places significant restrictions on slot machine ownership, but the law is widely flouted and slot machines are common in bars and coffeeshops.[34]

In regards to tribal casinos located on Native American reservations, slot machines played against the house and operating independently from a centralized computer system are classified as "Class III" gaming by the Indian Gaming Regulatory Act (IGRA), and sometimes promoted as "Vegas-style" slot machines.[35] In order to offer Class III gaming, tribes must enter into a compact (agreement) with the state that is approved by the Department of the Interior, which may contain restrictions on the types and quantity of such games. As a workaround, some casinos may operate slot machines as "Class II" games—a category that includes games where players play exclusively against at least one other opponent and not the house, such as bingo or any related games (such as pull-tabs). In these cases, the reels are an entertainment display with a pre-determined outcome based on a centralized game played against other players. Under the IGRA, Class II games are regulated by individual tribes and the National Indian Gaming Commission, and do not require any additional approval if the state already permits tribal gaming.[36][37]

Some historical race wagering terminals operate in a similar manner, with the machines using slots as an entertainment display for outcomes paid using the parimutuel betting system, based on results of randomly-selected, previously-held horse races (with the player able to view selected details about the race and adjust their picks before playing the credit, or otherwise use an auto-bet system).[38]

Alaska, Arizona, Arkansas, Kentucky, Maine, Minnesota, Nevada, Ohio, Rhode Island, Texas, Utah, Virginia, and West Virginia place no restrictions on private ownership of slot machines. Conversely, in Connecticut, Hawaii, Nebraska, South Carolina, and Tennessee, private ownership of any slot machine is completely prohibited. The remaining states allow slot machines of a certain age (typically 25–30 years) or slot machines manufactured before a specific date. For a detailed list of state-by-state regulations on private slot machine ownership, see U.S. state slot machine ownership regulations.

The Government of Canada has minimal involvement in gambling beyond the Canadian Criminal Code. In essence, the term "lottery scheme" used in the code means slot machines, bingo and table games normally associated with a casino. These fall under the jurisdiction of the province or territory without reference to the federal government; in practice, all Canadian provinces operate gaming boards that oversee lotteries, casinos and video lottery terminals under their jurisdiction.

OLG piloted a classification system for slot machines at the Grand River Raceway developed by University of Waterloo professor Kevin Harrigan, as part of its PlaySmart initiative for responsible gambling. Inspired by nutrition labels on foods, they displayed metrics such as volatility and frequency of payouts.[39]

In Australia "Poker Machines" or "pokies"[40] are officially termed "gaming machines". In Australia, gaming machines are a matter for state governments, so laws vary between states. Gaming machines are found in casinos (approximately one in each major city), pubs and clubs in some states (usually sports, social, or RSL clubs). The first Australian state to legalize this style of gambling was New South Wales, when in 1956 they were made legal in all registered clubs in the state. There are suggestions that the proliferation of poker machines has led to increased levels of problem gambling; however, the precise nature of this link is still open to research.[41]

In 1999 the Australian Productivity Commission reported that nearly half Australia's gaming machines were in New South Wales. At the time, 21% of all the gambling machines in the world were operating in Australia and, on a per capita basis, Australia had roughly five times as many gaming machines as the United States. Australia ranks 8th in total number of gaming machines after Japan, U.S.A., Italy, U.K., Spain and Germany. This primarily is because gaming machines have been legal in the state of New South Wales since 1956; over time, the number of machines has grown to 97,103 (at December 2010, including the Australian Capital Territory). By way of comparison, the U.S. State of Nevada, which legalised gaming including slots several decades before N.S.W., had 190,135 slots operating.[42]

Revenue from gaming machines in pubs and clubs accounts for more than half of the $4 billion in gambling revenue collected by state governments in fiscal year 2002–03.

In Queensland, gaming machines in pubs and clubs must provide a return rate of 85%, while machines located in casinos must provide a return rate of 90%. Most other states have similar provisions. In Victoria, gaming machines must provide a minimum return rate of 87% (including jackpot contribution), including machines in Crown Casino. As of December 1, 2007, Victoria banned gaming machines that accepted $100 notes; all gaming machines made since 2003 comply with this rule. This new law also banned machines with an automatic play option. One exception exists in Crown Casino for any player with a VIP loyalty card: they can still insert $100 notes and use an autoplay feature (whereby the machine will automatically play until credit is exhausted or the player intervenes). All gaming machines in Victoria have an information screen accessible to the user by pressing the "i key" button, showing the game rules, paytable, return to player percentage, and the top and bottom five combinations with their odds. These combinations are stated to be played on a minimum bet (usually 1 credit per line, with 1 line or reel played, although some newer machines do not have an option to play 1 line; some machines may only allow maximum lines to be played), excluding feature wins.

Western Australia has the most restrictive regulations on electronic gaming machines in general, with the Crown Perth casino resort being the only venue allowed to operate them,[43] and banning slot machines with spinning reels entirely. This policy had an extensive political history, reaffirmed by the 1974 Royal Commission into Gambling:[44]

Poker machine playing is a mindless, repetitive and insidious form of gambling which has many undesirable features. It requires no thought, no skill or social contact. The odds are never about winning. Watching people playing the machines over long periods of time, the impressionistic evidence at least is that they are addictive to many people. Historically poker machines have been banned from Western Australia and we consider that, in the public interest, they should stay banned.

While Western Australian gaming machines are similar to the other states', they do not have spinning reels. Therefore different animations are used in place of the spinning reels in order to display each game result.

Nick Xenophon was elected on an independent No Pokies ticket in the South Australian Legislative Council at the 1997 South Australian state election on 2.9 percent, re-elected at the 2006 election on 20.5 percent, and elected to the Australian Senate at the 2007 federal election on 14.8 percent. Independent candidate Andrew Wilkie, an anti-pokies campaigner, was elected to the Australian House of Representatives seat of Denison at the 2010 federal election. Wilkie was one of four crossbenchers who supported the Gillard Labor government following the hung parliament result. Wilkie immediately began forging ties with Xenophon as soon as it was apparent that he was elected. In exchange for Wilkie's support, the Labor government are attempting to implement precommitment technology for high-bet/high-intensity poker machines, against opposition from the Tony Abbott Coalition and Clubs Australia.

During the COVID-19 pandemic of 2020, every establishment in the country that facilitated poker machines was shut down, in an attempt to curb the spread of the virus. Bringing Australia's usage of poker machines effectively to zero.[45]

In Russia, "slot clubs" appeared quite late, only in 1992. Before 1992, slot machines were only in casinos and small shops, but later slot clubs began appearing all over the country. The most popular and numerous were "Vulcan 777" and "Taj Mahal". Since 2009 when gambling establishments were banned, almost all slot clubs disappeared and are found only in a specially authorized gambling zones.

Row of old fruit machines in Teignmouth Pier, Devon

One armed bandits at Wookey Hole Caves

Slot machines are covered by the Gambling Act 2005, which superseded the Gaming Act 1968.[46]

Slot machines in the U.K. are categorised by definitions produced by the Gambling Commission as part of the Gambling Act of 2005.

Casinos built under the provisions of the 1968 Act are allowed to house either up to twenty machines of categories B–D or any number of C–D machines. As defined by the 2005 Act, large casinos can have a maximum of one hundred and fifty machines in any combination of categories B–D (subject to a machine-to-table ratio of 5:1); small casinos can have a maximum of eighty machines in any combination of categories B–D (subject to a machine-to-table ratio of 2:1).

Category A games were defined in preparation for the planned "Super Casinos". Despite a lengthy bidding process with Manchester being chosen as the single planned location, the development was cancelled soon after Gordon Brown became Prime Minister of the United Kingdom. As a result, there are no lawful Category A games in the U.K.

Category B games are divided into subcategories. The differences between B1, B3 and B4 games are mainly the stake and prizes as defined in the above table. Category B2 games – Fixed odds betting terminals (FOBTs) – have quite different stake and prize rules: FOBTs are mainly found in licensed betting shops, or bookmakers, usually in the form of electronic roulette.

The games are based on a random number generator; thus each game's probability of getting the jackpot is independent of any other game: probabilities are all equal. If a pseudorandom number generator is used instead of a truly random one, probabilities are not independent since each number is determined at least in part by the one generated before it.

Category C games are often referred to as fruit machines, one-armed bandits and AWP (amusement with prize). Fruit machines are commonly found in pubs, clubs, and arcades. Machines commonly have three but can be found with four or five reels, each with 16–24 symbols printed around them. The reels are spun each play, from which the appearance of particular combinations of symbols result in payment of their associated winnings by the machine (or alternatively initiation of a subgame). These games often have many extra features, trails and subgames with opportunities to win money; usually more than can be won from just the payouts on the reel combinations.

Fruit machines in the U.K. almost universally have the following features, generally selected at random using a pseudorandom number generator:

• A player (known in the industry as a punter) may be given the opportunity to hold one or more reels before spinning, meaning they will not be spun but instead retain their displayed symbols yet otherwise count normally for that play. This can sometimes increase the chance of winning, especially if two or more reels are held.
• A player may also be given a number of nudges following a spin (or, in some machines, as a result in a subgame). A nudge is a step rotation of a reel chosen by the player (the machine may not allow all reels to be nudged for a particular play).
• Cheats can also be made available on the internet or through emailed newsletters to subscribers. These cheats give the player the impression of an advantage, whereas in reality the payout percentage remains exactly the same. The most widely used cheat is known as hold after a nudge and increases the chance that the player will win following an unsuccessful nudge. Machines from the early 1990s did not advertise the concept of hold after a nudge when this feature was first introduced, it became so well-known amongst players and widespread amongst new machine releases that it is now well-advertised on the machine during play. This is characterised by messages on the display such as DON'T HOLD ANY or LET 'EM SPIN and is a designed feature of the machine, not a cheat at all.

It is known for machines to pay out multiple jackpots, one after the other (this is known as a streak or rave) but each jackpot requires a new game to be played so as not to violate the law about the maximum payout on a single play. Typically this involves the player only pressing the Start button for which a single credit is taken, regardless of whether this causes the reels to spin or not. The minimum payout percentage is 70%, with pubs often setting the payout at around 78%.

Japanese slot machines, known as pachisuro (パチスロ) or pachislot from the words "pachinko" and "slot machine", are a descendant of the traditional Japanese pachinko game. Slot machines are a fairly new phenomenon and they can be found mostly in pachinko parlors and the adult sections of amusement arcades, known as game centers.

The machines are regulated with integrated circuits, and have six different levels changing the odds of a 777. The levels provide a rough outcome of between 90% to 160% (200% for skilled players). Japanese slot machines are "beatable". Parlor operators naturally set most machines to simply collect money, but intentionally place a few paying machines on the floor so that there will be at least someone winning, encouraging players on the losing machines to keep gambling, using the psychology of the gambler's fallacy.

Despite the many varieties of pachislot machines, there are certain rules and regulations put forward by the Security Electronics and Communication Technology Association (保安電子通信技術協会), an affiliate of the National Police Agency. For example, there must be three reels. All reels must be accompanied by buttons which allow players to manually stop them, reels may not spin faster than 80 RPM, and reels must stop within 0.19 seconds of a button press. In practice, this means that machines cannot let reels slip more than 4 symbols. Other rules include a 15 coin payout cap, a 50 credit cap on machines, a 3 coin maximum bet, and other such regulations.

Although a 15 coin payout may seem quite low, regulations allow "Big Bonus" (c. 400–711 coins) and "Regular Bonus" modes (c. 110 coins) where these 15 coin payouts occur nearly continuously until the bonus mode is finished. While the machine is in bonus mode, the player is entertained with special winning scenes on the LCD display, and energizing music is heard, payout after payout.

Three other unique features of Pachisuro machines are "stock", "renchan", and tenjō (天井). On many machines, when enough money to afford a bonus is taken in, the bonus is not immediately awarded. Typically the game merely stops making the reels slip off the bonus symbols for a few games. If the player fails to hit the bonus during these "standby games", it is added to the "stock" for later collection. Many current games, after finishing a bonus round, set the probability to release additional stock (gained from earlier players failing to get a bonus last time the machine stopped making the reels slip for a bit) very high for the first few games. As a result, a lucky player may get to play several bonus rounds in a row (a "renchan"), making payouts of 5,000 or even 10,000 coins possible. The lure of "stock" waiting in the machine, and the possibility of "renchan" tease the gambler to keep feeding the machine. To tease them further, there is a tenjō (ceiling), a maximum limit on the number of games between "stock" release. For example, if the tenjō is 1,500, and the number of games played since the last bonus is 1,490, the player is guaranteed to release a bonus within just 10 games.

Because of the "stock", "renchan", and tenjō systems, it is possible to make money by simply playing machines on which someone has just lost a huge amount of money. This is called being a "hyena". They are easy to recognize, roaming the aisles for a "kamo" ("sucker" in English) to leave his machine.

In short, the regulations allowing "stock", "renchan", and tenjō transformed the pachisuro from a low-stakes form of entertainment just a few years back to hardcore gambling. Many people may be gambling more than they can afford, and the big payouts also lure unsavory "hyena" types into the gambling halls.

To address these social issues, a new regulation (Version 5.0) was adopted in 2006 which caps the maximum amount of "stock" a machine can hold to around 2,000–3,000 coins' worth of bonus games. Moreover, all pachisuro machines must be re-evaluated for regulation compliance every three years. Version 4.0 came out in 2004, so that means all those machines with the up to 10,000 coin payouts will be removed from service by 2007.