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A slot machine (American English), known variously as a fruit machine (British English, except Scotland), puggy (Scottish English), the slots (Canadian and American English), poker machine/pokies (Australian English and New Zealand English), or simply slot (British English and American English), is a casino gambling machine that creates a game of chance for its customers.
Its standard layout is a display with three or more reels which rotate when a lever is pulled or button pushed. Slot machines are also known as one-armed banditsbecause they were originally operated by pulling upon a large mechanical lever on the side of the machine (as distinct from the modern button on the front panel), and because of their ability to empty a player’s pockets and wallet as a thief would. Many modern machines are still equipped with a legacy lever in addition to the button.
Slot machines include one or more currency detectors that validate the form of payment, whether coin, cash, or token. The machine pays off according to patterns of symbols appearing on its display when it stops. Slot machines are the most popular gambling method in casinos and constitute about 70 percent of the average US casino’s income.
Digital technology has resulted in variations on the original slot machine concept. Since the player is essentially playing a video game, manufacturers are able to offer more interactive elements, such as advanced bonus rounds and more varied video graphics.
Bonus is a special feature of the particular game theme, which is activated when certain symbols appear in a winning combination. Bonuses vary depending upon the game. Some bonus rounds are a special session of free spins (the number of which is often based on the winning combination that triggers the bonus), often with a different or modified set of winning combinations as the main game, and often with winning credit values increased by a specific multiplier, which is prominently displayed as part of the bonus graphics and/or animation (which in many cases is of a slightly different design or color scheme from the main game). In other bonus rounds, the player is presented with several items on a screen from which to choose. As the player chooses items, a number of credits is revealed and awarded. Some bonuses use a mechanical device, such as a spinning wheel, that works in conjunction with the bonus to display the amount won. (Some machines feature two or more of these bonus styles as part of the same game.)
Candle is a light on top of the slot machine. It flashes to alert the operator that change is needed, hand pay is requested or a potential problem with the machine. It can be lit by the player by pressing the “service” or “help” button.
Carousel refers to a grouping of slot machines, usually in a circle or oval formation.
Coin hopper is a container where the coins that are immediately available for payouts are held. The hopper is a mechanical device that rotates coins into the coin tray when a player collects credits/coins (by pressing a “Cash Out” button). When a certain preset coin capacity is reached, a coin diverter automatically redirects, or “drops,” excess coins into a “drop bucket” or “drop box.” (Unused coin hoppers can still be found even on games that exclusively employ Ticket-In Ticket-Out technology, as a vestige.)
Credit meter is a visual LED display of the amount of money or number of credits on the machine. On video reel machines this is either a simulated LED display, or represented in a different font altogether, based on the design of the game graphics.
Drop bucket or drop box is a container located in a slot machine’s base where excess coins are diverted from the hopper. Typically, a drop bucket is used for low denomination slot machines and a drop box is used for high denomination slot machines. A drop box contains a hinged lid with one or more locks whereas a drop bucket does not contain a lid. The contents of drop buckets and drop boxes are collected and counted by the casino on a scheduled basis.
EGM is used as a shorthand for “Electronic Gaming Machine”.
Free Spin is a term used in slot games and online slot games to specify that the spin will be completed without a charge or on the same wager. Free spins can get triggered by a number of things, each game uses a different method. Usually, landing a number of special symbols on reels is required to activate the free spins bonus round. Mostly scatter symbols are preferred for this activation, although wild symbols (or a completely different symbol dedicated for this feature) can be used too. In most slot games, landing at least three special symbols on reels is mandatory to trigger the feature. Once triggered, free spins bonus round award a number of spins free of charge to the player. The number of free spins differ from game to game. If there is the ability to re-trigger free spins during the free spin bonus there is no theoretical limit to the number of free spins obtainable. The spins are automatically used by the game and the player keeps any profit after the spins are complete. A single free spin is sometimes called a respin.
Hand pay refers to a payout made by an attendant or at an exchange point (“cage”), rather than by the slot machine itself. A hand pay occurs when the amount of the payout exceeds the maximum amount that was preset by the slot machine’s operator. Usually, the maximum amount is set at the level where the operator must begin to deduct taxes. A hand pay could also be necessary as a result of a short pay.
Hopper fill slip is a document used to record the replenishment of the coin in the coin hopper after it becomes depleted as a result of making payouts to players. The slip indicates the amount of coin placed into the hoppers, as well as the signatures of the employees involved in the transaction, the slot machine number and the location and the date.
MEAL book (Machine entry authorization log) is a log of the employee’s entries into the machine.
Low Level or Slant Top slot machines include a stool so the player has sitdown access. Stand Up or Upright slot machines are played while standing.
Optimal play is a payback percentage based on a gambler using the optimal strategy in a skill-based slot machine game.
Payline is a line that crosses through one symbol on each reel, along which a winning combination is evaluated. Classic spinning reel machines usually have up to nine paylines, while video slot machines may have as many as one hundred. Paylines could be of various shapes (horizontal, vertical, oblique, triangular, zigzag, etc.)
Rollup is the process of dramatizing a win by playing sounds while the meters count up to the amount that has been won.
Short pay refers to a partial payout made by a slot machine, which is less than the amount due to the player. This occurs if the coin hopper has been depleted as a result of making earlier payouts to players. The remaining amount due to the player is either paid as a hand pay or an attendant will come and refill the machine.
Scatter Symbol It is required to place at least two of the same symbols on a pay line to get paid in slot games. However, scatter symbols work differently and award a prize whether they are placed on a pay line or not. But the player still needs to get at least two of them in modern slot games. (The more, the better.) Scatter symbols are usually used to award a number of free spins. The number of free spins differs from game to game; i.e. 20 free spins for landing 3 scatter symbols anywhere on reels. They can also award coin prizes, based on their number. The prizes are usually small, but they are paid in addition to other winnings. The scatter symbol is usually a special symbol, which means the wild symbol cannot replace it, although in some games the wild symbol also substitutes for scatters.
Slot Variance At the heart of slot machine gameplay is the concept of slot variance (or slot volatility) that is fundamental to how a slot machine ‘feels’ to play. Slot variance is a measure of risk associated with playing a slot machine. A low variance slot machine has regular but smaller wins and a high variance slot machine has fewer but bigger wins.
Taste is a reference to the small amount often paid out to keep a player seated and continuously betting. Only rarely will machines fail to pay out even the minimum placed a bet over the course of several pulls.
Tilt Electromechanical slot machines usually include an electromechanical “tilt switch”, which makes or breaks a circuit if the machine is tilted or otherwise tampered with, and so triggers an alarm. While modern machines no longer have tilt switches, any kind of technical fault (door switch in the wrong state, reel motor failure, out of paper, etc.) is still called a “tilt”.
Theoretical Hold Worksheet A document provided by the manufacturer for all slot machines, which indicates the theoretical percentage that the slot machine should hold based on the amount paid in. The worksheet also indicates the reel strip settings, number of coins that may be played, the payout schedule, the number of reels and other information descriptive of the particular type of slot machine.
Weight count is an American term, referring to the dollar amount of coins or tokens removed from a slot machine’s drop bucket or drop box and counted by the casino’s hard count team through the use of a weigh scale.
Wild Symbol Wild symbols act like joker cards in a slot game. Basically, they substitute for all other symbols in the game, usually except for other special symbols, such as scatter and jackpot. They can appear on any of the reels. However, this is not mandatory and can be changed from game to game. In some games, wild symbols can appear only on certain reels. Or, they can appear only during the bonus rounds. The player must refer to the rules and paytable of the game to learn about the landing rules. In online slot games, they can also be used for winning a jackpot, multiplying the prize and/or triggering a certain feature.
Mobile is when the slot machine is hosted for online gambling and it is usually available for use on a phone, tablet, or other portable device. These are often standalone mobile casino applications but are also found as part of the online casino site. See Mobile gambling. By 2017, HTML5 technology and the advancement of mobile browsers had negated the need for standalone mobile apps. New slots are, by majority, playable on both mobile and desktop devices.
Each machine has a table that lists the number of credits the player will receive if the symbols listed on the pay table line up on the pay line of the machine. Some symbols are wild and can represent many, or all, of the other symbols to complete a winning line. Especially on older machines, the pay table is listed on the face of the machine, usually above and below the area containing the wheels. Most video machines display the pay table when the player presses a “pay table” button or touches “pay table” on the screen; some have the pay table listed on the cabinet as well.
Random number generators
All modern machines are designed using pseudo random 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, 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 82% to 98% 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 played 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, that 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!” It is worth noting that the “Loose Slots” actually may describe a very few anonymous machines in a particular bank of EGMs.
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 Shacklefordrevealed 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 midsize 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 his 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 midsize payouts, but unlikely to have a large payout. He quits after he is bored or has exhausted his bankroll.
Despite the fact that they are confidential, 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.