Slot Fairness and Random Results

Slots are the most popular gambling game, generating as much as 70% of the casino operators’ revenue worldwide. Slot machines have been around for over a century now and have undergone many changes since they first emerged. The invention of the microchip completely changed the way slots play and pay.

The early machines were purely mechanical and relied on physical strips of symbols called reels. After the player inserted credits into the coin slit and pulled the lever, the reels were spun. Mechanical machines featured fewer symbols because space on the physical reels was limited.

The modern slots we play today utilize virtual reels with unlimited space. This allows for the addition of a higher number of symbols, which in turn increases the number of possible combinations, allowing slot developers to experiment with different odds, volatility, and payback percentages. The outcomes of the spins are determined by microchips that produce fair results based on random number generation.

The Randomization of Results in Slot Games

1How RNG Works

All modern video slots operate with the help of computer microchips programmed to generate random numbers. The Random Number Generator (RNG) spits between 1 and several billion random numbers every single second of the day and night.

This happens even when no one is spinning the reels of the slot. The random number generation continues endlessly as long as the slot machine is plugged in. These random numbers determine the position of the reels when they come to rest.

It is important to understand that the player is not initiating anything by the press of a button. The reels are set in motion for authenticity but the result has already been decided in the exact millisecond the spin button was pressed.

The RNG assigns a numerical value to each symbol the reels contain and uses sophisticated algorithms to produce the outcome of each spin. After you press the spin button, the RNG generates random numbers for each reel to determine what symbols appear on the reel grids. If any of the generated symbols match and align on a payline, the machine awards the corresponding payout.

It is preprogrammed in a way so that the odds remain the same for each spin of the reels. The algorithms are so complex that the player cannot discern any predictable pattern in the occurrence of the outcomes. In essence, this means you are playing a random game.

Slot machines have no hot or cold cycles because the results are decided on a random principle. The RNG is preprogrammed to yield specific average payout percentages and hit frequencies in the long term.

2How RNG yields a payout?

To give you a better idea of how an RNG yields a payout, let’s go through a simple scenario where you have a slot with three reels, twenty symbols on each reel, and twenty spaces. Each reel contains 1 bell, 2 bars, 3 cherries, 4 plums, 5 lemons, and 5 oranges.

The number of possible combinations here is 40 x 40 x 40 = 64,000. The RNG would assign a number to each symbol on the reel so that it has a total of 135 stops.

Reel Symbol Total Stops for the Symbol Random Numbers for Symbol
Bell (pays jackpot) 1 stop 1
Bar 1 3 stops 2, 3, 4
Bar 2 3 stops 5, 6, 7
Cherry 1 5 stops 8, 9, 10, 11, 12
Cherry 2 5 stops 13, 14, 15, 16, 17
Cherry 3 5 stops 18, 19, 20, 21, 22
Plum 1 7 stops 23, 24, 25, 26, 27, 28, 29
Plum 2 7 stops 30, 31, 32, 33, 34, 35, 36
Plum 3 7 stops 37, 38, 39, 40, 41, 42, 43
Plum 4 7 stops 44, 45, 46, 47, 48, 49, 50
Lemon 1 8 stops 51, 52, 53, 54, 55, 56, 57, 58
Lemon 2 8 stops 59, 60, 61, 62, 63, 64, 65, 66
Lemon 3 8 stops 67, 68, 69, 70, 71, 72, 73, 74
Lemon 4 8 stops 75, 76, 77, 78, 79, 80, 81, 82
Lemon 5 8 stops 83, 84, 85, 86, 87, 88, 89, 90
Orange 1 9 stops 91, 92, 93, 94, 95, 96, 97, 98, 99
Orange 2 9 stops 100, 101, 102, 103, 104, 105, 106, 107, 108
Orange 3 9 stops 109, 110, 111, 112, 113, 114, 115, 116, 117
Orange 4 9 stops 118, 119, 120, 121, 122, 123, 124, 125, 126
Orange 5 9 stops 127, 128, 129, 130, 131, 132, 133, 134, 135

We used an example where identical symbols on the reel have the same number of stops. However, symbol mapping does not necessarily have to be the same on all reels. The spaces are also considered stops but we used only the symbols for simplicity.

The Random Number Generator would assign a value from 1 to 135 to each of the three reels. If it chooses 110 for the first reel, 134 for the second reel, and 100 for the third reel, you would have a combination of three oranges.

The game awards a given number of credits if the combination has fallen onto a winning line. The more stops per reel a given symbol has, the higher its odds of occurrence. Of course, the software in advanced slots can map a greater number of symbols and stops on the reels. Such games can yield millions and even billions of possible combinations, which leaves room for much larger jackpots.

Pseudo vs. True Random Number Generators

Pseudo RNG
True RNG

There are two types of Random Number Generators but those used in most modern slots (and online casino games in general) are pseudo RNGs. The unique thing about the pseudo RNG is that it creates an output, i.e. an outcome, without using external data. It relies solely on a complex algorithm, a set of predetermined constants, and a seed. The seed number is of extreme importance here because it defines the starting point when the RNG generates a string of random numbers.

True Random Number Generators (also known as Hardware Random Number Generators) are capable of producing results that are indeed unpredictable. This type of RNG does not rely on seed values because the results it yields are never derived from repeatable algorithms.

Seed numbers are necessary in this case because computer programs are incapable of generating truly random numbers. They rely on a set of specific rules, i.e. algorithms, to mimic randomness. As complex as these algorithms are, they still follow a pattern. Thus, a sequence of random numbers can be reproduced if one knows the initial seed value.

Rather, it derives random numbers from digitized images of naturally occurring phenomena, such as atmospheric and thermal noise or the decay of radioactive elements. Any source of natural entropy will do.

The pseudo RNG uses mathematics but there is nothing random about mathematic calculations. A given input would inevitably produce the same output. Moreover, the random number sequence is bound to repeat itself after a certain number of trials, which makes it easier for gaming auditors to inspect the slots for fairness.

One of the main reasons why true RNGs are superior to their pseudo counterparts is that the former are insusceptible to hacking. Since no repeatable algorithms are involved here, a hacker would be unable to predict future numbers even if they manage to figure out one number.

This is not to say that a slot player can discern this pattern and deduce when it is about to repeat. The RNG spews seeds every millisecond. It normally takes one or two numbers it has generated last and uses them as part of a mathematical operation to produce a new random result.

With that in mind, true RNGs are more costly from the casinos' perspective. Like all material objects, hardware components are subject to entropy. They tend to wear and tear over time and therefore are more expensive to maintain.

How Preprogrammed Slot Games Still Yield Random Results

1Predetermined theoretical payback percentages

It is a well-known fact that slots have predetermined theoretical payback percentages. In other words, they are preprogrammed to return a specific percentage of all wagers made back to the players while the casino gets to keep the remainder.

For example, if a given slot has a listed theoretical return of 96.50%, it will produce a house edge of 3.50%. Over time, one such game will pay back the cumulative amount of $96.50 while the house will retain $3.50 out of every $100 wagered on this particular machine. Of course, it takes a very long time and thousands of spins until return percentages and house edges begin to manifest themselves.

2Preprogrammed and random at the same time

This programming causes some players to question the randomness of the games. They ask themselves how can a slot be preprogrammed and random at the same time. This is indeed possible because slots are programmed to return a target percentage the same way table games like craps and roulette are.

Their odds are adjusted in such a way so that the game always generates its expected return percentage. The slots are designed so that blank spaces appear more frequently than winning symbols. Respectively, the low-paying winning combinations are set to land more often than high-paying ones.

The player will experience more losing rounds than winning ones on classic three-reel slots, and a person who plays five-reel video slots would register more wins for amounts smaller than the size of their wager than high-paying combinations.

3Determination of the odds

The game makers only determine the odds and let the RNG take care of the randomness of results. When gambling operators purchase machines from a given slot vendor, they can pick from several targeted return percentages.

The same slot can be designed to pay back 89%, 91% or 94%, depending on the preferences of the gambling operator. Of course, these return percentages must fit into the requirements of the casino’s local regulatory body.

Can You Beat the Random Number Generator in Slots?

Another commonly asked question is whether players can beat a slot's Random Number Generator. The short answer is this is technically possible, although very few people can actually achieve it.

As we previously explained, some slots use pseudo Random Number Generators which rely on mathematical algorithms to produce unpredictable outcomes. This makes them susceptible to the attacks of hackers, but of course one needs to be a genius in the field of computer programming to succeed.

Nevada Regulator's Employee Reprograms the RNG
Russian Hackers Unpuzzle Secret of the RNG

Nevada Regulator's Employee Reprograms the RNG

There are two cases of people beating the slot RNG that come to mind. The first one involved a programmer by the name of Ronald Harris who worked for the Nevada Gaming Control Board and took advantage of his position in the early 1990s.

Harris was tasked with analyzing the software of slot machines across Las Vegas casinos for flaws. Being an expert in his field, it did not take him long to see the machines could be tampered with so that they generate consistent winnings.

As an employee of the local regulator, Harris was privy to the confidential code used to reprogram the RNGs of slots. He decided to reprogram machines so that they paid out certain amounts of money when coins were inserted in a specific order. One of the insertion sequences he used was 3 coins on the first spin, 2 coins on of the second and third spins, 1 coin on the fourth spin, 6 coins on the fifth spin, and then 5 coins on the sixth spin.

This sequence ensured substantial wins. The only trouble was Harris was not allowed to gamble at all because he was employed by the Nevada regulator. To circumvent this obstacle, Harris decided to get in touch with a close friend of his who had recently lost his job.

The task of Reid McNeal, the friend in question, was to insert coins into certain machines in the same order Harris had specified. The profits the two generated were divided evenly. Things quickly took off for the scammers, so much so that they moved their operations to Atlantic City to avoid detection.

They were winning decent amounts at the time but greed took its toll on them. In 1995, Harris decided to transition from slots to keno machines. The managers of Atlantic City’s Bally Park Place Hotel and Casino grew suspicious after his partner won $100,000 at keno with an investment of as little as $100.

This stint earned Harris a jail sentence of seven years but he was released on good behavior after serving two years only. He was also added to the black book of the Nevada Gaming Control Board and was prohibited from entering a Nevada casino ever again.

Russian Hackers Unpuzzle Secret of the RNG

In June 2014, the accountants of St. Louis’ Lumière Place Casino noticed several of their slot machines behaved rather strangely. The slots in question had returned more money than was expected of them in just two days. No large jackpots had hit during those two days, either.

Since the machines relied on a complex predetermined code that does not change from day to day, the only possible explanation for this oddity was that someone had cheated.

After careful examination of surveillance footage, the casino management spotted a man who behaved strangely although he did not fit the typical profile of a slot cheater. The man in question was 37-year-old Russian Murat Bliev, who operated as part of a larger group of cheats.

Bliev would hold his mobile phone close to the machine’s screen and then would get up seemingly ready to leave. He would come back several minutes later to try his luck one last time. For one reason or another, his decision to return always paid off well. He managed to extract around $21,000 from the casino in just two days.

After an extensive investigation by the Missouri Gaming Commission, it was established that other gambling establishments were also cheated similarly but by different people, who operated as a crew in casinos across the United States, Europe, and Macau.

Bliev and one of his associates were eventually detained and confessed to the whole scheme. After Russia outlawed gambling in 2008, many casinos in the country started to sell their gaming equipment to whoever was willing to buy it. This is how some slot machines manufactured by Aristocrat ended up in the hands of the hacker group Bliev was working for.

The hackers carefully examined the slots and succeeded in reverse-engineering their Random Number Generators. This knowledge of the machines’ code enabled them to identify patterns in the outcomes and use this information to their advantage.

The way it worked was the group’s associates were sent to scan the casino floors for particular machines. They would then record several dozens of spins and upload them to the crew in Saint Petersburg.

The crew analyzed the results to identify current spin patterns and establish the optimal moment when the odds were tipped in favor of the player. Then they would relay a list of timing markers to their partners’ phones. A special, custom-designed mobile app was used for this purpose. The player’s phone would start vibrating a fraction of a second before they had to press the button for the winning spin.

While this approach was not effective 100% of the time, it still allowed the players to pocket abnormally high payouts. To avoid detection, a scammer would extract only around $1,000 at a time from each hacked machine. Nevertheless, a group of four associates still managed to rake in weekly profits of around $250,000.

Who Ensures the Fairness of Slot Random Number Generators

Independent testing agencies

The badge for fairness

Casinos cannot change the RTP at will

To preserve the integrity of their business, all legally operating casinos would subject their slots to frequent audits. The tests are conducted by independent testing agencies like Technical Systems Testing (TST), eCOGRA, and iTech Labs.

These companies offer a broad range of consulting and testing services, including RNG evaluations which involve hundreds of thousands of spins. The outcomes are then analyzed to ensure the slots indeed live up to their expected theoretical return percentages.

It is essential to specify that these percentages correspond to an average achieved over a significant number of spins and not each time a given person plays the machine. According to the UK Gambling Commission, the average return percentage is measured over 10,000 or 100,000 spins, often even more.

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