Random Number Generator
Modern slot machines are computerized. The odds are programmed. In modern slot machines, the reels and lever are present for historical and entertainment reasons only. The positions of the reels depend on a Random Number Generator. The machine's software includes a Random Number Generator.
The RNG generates random numbers at an extremely high rate. The most recent random number is used to determine the result when the Play button is pressed. That means that the result depends on exactly when the game is played. A fraction of a second earlier or later, and the result would be different.
The numbers generated by the RNG seem to be not exactly random. It turned out that The number sequence is repeated time after time. This behavior is due to poor programming. To build pseudo RNGs with very long periods is relatively easy. The computer that is able to complete a single period in the expected lifetime of the universe hasn't been invented yet. The access to the pseudo RNG code and seed values was known to Ronald Dale Harris, a former slot machine programmer. It was he who discovered equations for specific gambling games like Keno. The fact that the next set of selected numbers would be based on the previous games played was revealed. But the RNG picks numbers even when the machine is not being played. So the numbers can't be exactly found in a sequence.

Percentage Of The Payout
Slot machines are typically programmed to pay out as winnings 82–98 per cent of the money that is wagered by players. This is known as the theoretical payout percentage. Jurisdictions influence the minimum theoretical payout percentage. It is typically established by law or regulation. A certain winning pattern is determined by every casino individually. It concerns the amounts they pay and the frequencies of these pay-outs. The winning patterns on slot machines are carefully selected to yield a certain fraction of the money played to the house. The players get the rest of the money.
A slot machine's theoretical payout percentage is set at the factory when the software is written. To change the payout percentage after a slot machine has been placed on the gaming floor a physical swap of the software is required. It is done infrequently because this is a time-consuming process. One can find a tamper-evident seal on the EPROM in certain jurisdictions. It can only be changed in the presence of Gaming Control Board officials. According to other jurisdictions slot machines are randomly audited to ensure that they contain only approved software.
Thanks to the newly developed technology the game, the odds, and the payouts would be able to be changed by the casino's slot manager remotely. The change can be done 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.

Machines Linking
Offering of a particularly large prize, or jackpot becomes possible when a group of machines is linked in a special way. If a player gets a specific combination of symbols the progressive jackpot from this group of machines is given to him. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own.
Sometimes multiple machines form multiple casinos. In these cases, the machines may be owned by the manufacturer, who is responsible for paying the jackpot.

Near-miss
The reel display of modern slot machines is under computer software's control. That is why the slot machine can be programmed to display combinations that are close to winning combinations.
Such showing combinations that are similar to winning combinations more frequently than would occur randomly is called near-miss programming.
There is a related phenomenon that is also sometimes called near-miss. It is winning percentages that control the chance of a winning combination appearing on a pay line. However, the combinations appearing above and below the pay line are all roughly equally randomly distributed. This means it is much more likely that a winning combination will appear above or below a pay line than on the pay line. This occurs if abbreviated physical reels are used to display a win pattern based upon the RNG. In video slot machines the symbols that appear around the winning line are usually an accurate depiction of how the reels were mathematically modeled.
The issue of a near-miss above or below the pay line was also investigated by the Nevada Gaming Commission. It was considered to be legal as long as the near-miss above or below the pay line was not specially programmed. In other words, the near-miss must be just as likely to occur as any other combination. It is impossible to program the machine to show winning combinations more frequently than other combinations above or below the pay line.
In Australia near-miss programming, where a near miss is inaccurately displayed is not allowed either. Due to this, regulators use stop motion cameras to audit manufacturer's practices.

Slot Machines Fraud
Mechanical slot machines and their coin acceptors were sometimes susceptible to cheating devices and other scams.
EPROM computer chips controls modern slot machines and coin acceptors have become obsolete in favor of bill acceptors. They are designed with advanced anti-cheating and anti-counterfeiting measures and are difficult to defraud. An example of modern ways of slot machine defrauding is directing microwaves toward it to disrupt its proper functioning.

Here is the list of the most amusing myths concerning slots.
You can spot a winning slot machine.
The only way one can say that theslot machine is a winning one is only to catch this moment, when the machine pays out. Slot machines use random numbergenerator and that's exactly that. Random.
Casinos place loose slots near the cashier, aisle ways, etc.
If this were true, it would be the only machines anyone would play. A casino mixes slots all over the casino floor. No one with any experience at playing slots would make a statement like this.
Count the number of symbols on the reels to determine your odds.
It is a rude mistake. RNG decides when the machine will stop and there are thousands of combination available on a 3 reel slot machine.
Casinos can tighten or loosen slot machines from the back office.
It is not as simple as that. The casino can’t just change the chip of the slot machine. It is illegal and it has to be permitted by the commission.
A slot machine that has not been paying is due to hit.
Absolutely false. The RNG assures this. You have an equal chance of winning on a losing machine as you do on a machine that just paid out the jackpot.
Pulling the slot machine handle produces more wins than pressing the spin button and visa versa.
Again false. It makes no difference, as the computer only uses these as mechanisms to start the game. Only the computer determines a win or a loss and it has already determined if you are a winner or loser even before the first reel stops spinning.
Playing with hot coins improves your chances.
Once again, the computer determines a win or loss and the temperature of the machine or moneyirrelevant. Although it's funny that people still burn their fingers with lighters believing this works.
Casinos set slot machines to payback more on the weekends.
One more rude mistake. The chances and odds are always the same. It doesn’t matter when you play.

Slot machines are honest because state gaming commissions make sure they are. However, in the past certain manufacturers have been caught using computer chips that cheat the customer.
In the old days, slot machines worked mechanically, with independent wheels spinning until they each stopped randomly. Modern slot machines differ form the old ones greatly. There is a chip inside of every slot machine, this chip is programmed to select numbers randomly. The numbers the computer selects correspond to the symbols that appear on the slot machine’s screen. There is a computer code. It generates the random numbers and determines whether the slot machine is loose or tight. The gaming inspector will examine the machine to make sure it will not deceive the player. There is a legal rate according to which the machine has to pay out. Of course it can pay lower, which happen very seldom.
It is next to impossible to say whether the chip is programmed not in a right way because the machine is not supposed to pay out with every spin. The machines have to be examined before people begin to play them. Of course it is very difficult to examine every single machine, that’s why inspectors examine only brands. Once inspectors approve a brand of machine, the manufacturers can make changes to individual machines as long as the changes fall within the legal bounds. Using their right to produce slot machines they insert different chips, which makes the machine pay less.
There is an example when there was inserted an illegal tip which doesn’t allow royal flushes. Similarly, Universal Distributing Company was caught programming machines to show a “near miss” of a jackpot. The player would never hit a jackpot but keep on playing maximum bets. Don’t keep silent if you come across such slot machine. Inspectors will respond by pulling the slot machine’s chip and seeing if it is an approved chip. Manufacturers that cheat are fined or they can lose their license.