Editing Slot machine (section)

==Technology==
===Reels===
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 [[cube (algebra)|cubic]] – the original slot machine with three physical reels and 10 symbols on each reel had only 10<sup>3</sup> = 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,<ref>{{cite web|url=http://gaming.unlv.edu/reading/Pacyniak.PDF|title=Info|website=gaming.unlv.edu|archive-url=https://web.archive.org/web/20060909064726/http://gaming.unlv.edu/reading/Pacyniak.PDF|archive-date=2006-09-09|url-status=live}}</ref> 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),<ref>{{US patent|4448419|Electronic gaming device utilizing a random number generator for selecting the reel stop positions}}</ref> 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."<ref>
{{cite journal|last=Collier|first=Roger|date=1 July 2008|title=Do slot machines play mind games with gamblers?|journal=Canadian Medical Association Journal|volume=179|issue=1|pages=23–4|doi=10.1503/cmaj.080870|pmc=2464464|pmid=18591518}}</ref> The patent was later bought by [[International Game Technology (1975–2015)|International Game Technology]] and has since expired.

A virtual reel that has 256 virtual stops per reel would allow up to 256<sup>3</sup> = 16,777,216 final positions. The manufacturer could choose to offer a $1 million jackpot on a $1 bet, confident that it will only happen, over the long term, once every 16.8 million plays.

===Computerization===
With [[microprocessor]]s 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===
Video slot machines do not use mechanical reels, but use graphical reels on a computerized [[Display device|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 [[minigame]]s as bonuses. Modern cabinets typically use [[flat-panel display]]s, but cabinets using larger [[curved screen]]s (which can provide a more immersive experience for the player) are not uncommon.<ref>{{Cite web|url=https://www.theverge.com/2015/5/6/8544303/casino-slot-machine-gambling-addiction-psychology-mobile-games|title=Slot machines perfected addictive gaming. Now, tech wants their tricks|last=Thompson|first=Andrew|date=2015-05-06|website=The Verge|language=en-US|access-date=2019-11-30}}</ref>

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 desired – 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 they are losing, the bonus game could allow them to win back their losses.

===Payout percentage===
{{Globalize|section|date=April 2019}}
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!"{{citation needed|date=March 2020}}

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 ([[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. {{citation needed span|date=April 2019|text=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]] [[security seal|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.{{citation needed|date=August 2019}}

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 Game Technology (1975–2015)|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 64<sup>3</sup> = 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.{{citation needed|date=August 2019}}

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 (disambiguation)|Austin Powers]]'', ''Fortune Cookie'', ''Leopard Spots'' and ''[[Wheel of Fortune (American game show)|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).{{citation needed|date=August 2019}}

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 network]]s 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.<ref>{{cite news|last=Richtel|first=Matt|date=12 April 2009|title=From the Back Office, a Casino Can Change the Slot Machine in Seconds|newspaper=[[The New York Times]]|url=https://www.nytimes.com/2006/04/12/technology/12casino.html?ei=5089&en=9e945a28ba5016c6&ex=1302494400&partner=rssyahoo&emc=rss&pagewanted=all|access-date=10 December 2009}}</ref>

===Linked machines===
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 jackpot]]s that are shared between the bank of machines, but may include multiplayer bonuses and other features.<ref>{{Cite web|url=https://www.casinojournal.com/articles/89815-the-latest-community-slot-games-offer-play-mechanics-and-features-designed-to-overcome-the-shortfalls-of-previous-products-and-concepts?v=preview|archive-url=https://web.archive.org/web/20170425070853/http://www.casinojournal.com/articles/89815-the-latest-community-slot-games-offer-play-mechanics-and-features-designed-to-overcome-the-shortfalls-of-previous-products-and-concepts?v=preview|url-status=usurped|archive-date=April 25, 2017|title=The latest community slot games offer play mechanics and features designed to overcome the shortfalls of previous products and concepts|website=Casino Journal|date=8 May 2015 |language=en|access-date=2019-12-03}}</ref>

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, Louisiana, Arkansas, and [[South Dakota]] now offer multi-state progressive jackpots, which now offer bigger jackpot pools.<ref>{{cite web|title=Division of Gaming Enforcement Announces Approval for Interstate Progressive Slot Machines|url=http://www.nj.gov/oag/ge/2014news/MultistateProgressiveSlotMachines.pdf|website=New Jersey Division of Gaming Enforcement|archive-url=https://web.archive.org/web/20140701174626/http://www.nj.gov/oag/ge/2014news/MultistateProgressiveSlotMachines.pdf|archive-date=2014-07-01|url-status=live}}</ref><ref>{{cite web|title=Division of Gaming Enforcement Announces Interstate Progressive Slots Link with Nevada|url=http://www.nj.gov/oag/ge/2014news/Multistate%20ProgressiveSlots.pdf|website=New Jersey Division of Gaming Enforcement|archive-url=https://web.archive.org/web/20150221171452/http://www.nj.gov/oag/ge/2014news/Multistate%20ProgressiveSlots.pdf|archive-date=2015-02-21|url-status=live}}</ref>

===Fraud===
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.<ref>{{cite news|url=http://usatoday30.usatoday.com/tech/news/2003-08-11-slot-cheats_x.htm|title=Slot machine cheat bilked casinos with ingenious gadgets|newspaper=USAToday.com |access-date=2014-06-08}}</ref>

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.<ref>{{Cite web|last=LaPointe|first=Michael|date=2020-02-04|title=The Edison of the Slot Machines|url=https://www.theparisreview.org/blog/2020/02/04/the-edison-of-the-slot-machines/|access-date=2020-10-08|website=The Paris Review|language=en}}</ref> In the modern day, computerized slot machines are fully deterministic and thus outcomes can be sometimes successfully predicted.<ref>{{cite magazine|last1=Koerner|first1=Brendan|title=Russians Engineer a Brilliant Slot Machine Cheat—And Casinos Have No Fix|url=https://www.wired.com/2017/02/russians-engineer-brilliant-slot-machine-cheat-casinos-no-fix|access-date=7 February 2017|magazine=[[Wired (magazine)|Wired]]|date=8 February 2017}}</ref>

===Skill stops===
Skill stop buttons predated the Bally electromechanical slot machines of the 1960s and 1970s. They appeared on mechanical slot machines manufactured by Mills Novelty Co. as early as the mid 1920s. These machines had modified reel-stop arms, which allowed them to be released from the timing bar, earlier than in a normal play, simply by pressing the buttons on the front of the machine, located between each reel.

"Skill stop" buttons were added to some slot machines by Zacharias Anthony in the early 1970s. These enabled the player to stop each reel, allowing a degree of "skill" so as to satisfy the [[New Jersey]] gaming laws of the day which required that players were able to control the game in some way. The original conversion was applied to approximately 50 late-model Bally slot machines. Because the typical machine stopped the reels automatically in less than 10 seconds, weights were added to the mechanical timers to prolong the automatic stopping of the reels. By the time the New Jersey Alcoholic Beverages Commission (ABC) had approved the conversion for use in New Jersey arcades, the word was out and every other distributor began adding skill stops. The machines were a huge hit on the [[Jersey Shore]] and the remaining unconverted Bally machines were destroyed as they had become instantly obsolete.{{Citation needed|date=March 2008}}