Random Number Generator
Modern slot machines are computerized. So the odds are whatever they are programmed to be. 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 is constantly generating random numbers at an extremely high rate. As soon as the Play button is pressed, the most recent random number is used to determine the result. 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. Most RNGs will repeat their number sequence. Poor programming determines such behavior. To build pseudo RNGs with very long periods is relatively easy. There is no computer that is able to complete a single period in the expected lifetime of the universe. Ronald Dale Harris, a former slot machine programmer, had access to the pseudo RNG code and seed values. Equations for specific gambling games like Keno were discovered by him. They allowed to predict that the next set of selected numbers would be based on the previous games played. However, this is impossible for most machines, because 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
The percentage of winnings paid out of the money that is wagered by players is 82–98 per cent. This is known as the theoretical payout percentage. Jurisdictions influence the minimum theoretical payout percentage. Its establishment refers to the sphere of law or regulation. A certain winning pattern exists nearly in every casino. It contains the information about the amounts they pay and the frequencies of these pay-outs. The selection of the slot machines winning patterns is chosen in such a way that it could yield a certain fraction of the money played to the house. As for the rest of the money it goes to the players.
When a slot machine's software is written its theoretical payout percentage is also set. Physical swap of the software is needed for changing the payout percentage after a slot machine has been placed on the gaming floor. It is done infrequently because this is a time-consuming process. In certain jurisdictions the EPROM has a tamper-evident seal. Gaming Control Board officials should be called for changing it. Other jurisdictions randomly audit slot machines to ensure that they contain only approved software.
The technology being developed by the Nevada Gaming Commission would allow the casino's slot manager 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.

Machines Linking
A group of machines offers a particularly large prize, or jackpot if they are linked together in a special way. Each slot machine in the group contributes a small amount to this progressive jackpot, awarded to a player who gets a specific combination of symbols. A single slot machine's jackpot is considerably less than the progressive jackpot.
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.

Near-miss Programming
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.
This practice of showing combinations that are similar to winning combinations more frequently than would occur randomly is called near-miss programming.
This term is also used for a related phenomenon. The chance of a winning combination appearing on a pay line is controlled by the winning percentages programmed into the slot machine. However, the combinations appearing above and below the pay line are all roughly equally randomly distributed. There are roughly equally randomly distributed combinations above and below the pay line. This phenomenon only occurs where abbreviated physical reels are used to display a win pattern based upon the RNG. Video slot machines have virtual reels and the symbols that appear around the winning line are usually an accurate depiction of how the reels were mathematically modeled.
The Nevada Gaming Commission investigated the issue of a near-miss above or below the pay line. It was considered to be legal as long as the near-miss above or below the pay line was not specially programmed. The near-miss and any other combination should have the same possibility of occurrence. The machine can't show winning combinations more frequently than other combinations above or below the pay line.
In Australia the usage of near-miss programming, where a near miss is inaccurately displayed is also illegal. Stop motion cameras are used by regulators for manufacturer's practices audit.

Slots Fraud
Mechanical slot machines and their coin acceptors were sometimes considered to be cheating devices and other scams.
Modern slot machines are controlled by EPROM computer chips and coin acceptors were changed for bill acceptors. Different advanced anti-cheating and anti-counterfeiting measures have been taken to make it difficult to defraud these machines. Recent attempts at defrauding slot machines involve manipulating the EPROM, such as by directing microwaves toward it to disrupt its proper functioning.

There are at least two types of slot players.
The first type is a persistent player.
This type of slots player is the one that believes the win is right around the corner. The machine can begin paying in any second.
The player has either seen a person playing a slots game for a while with no payouts or alternatively they have been depositing funds into a slots game and haven’t yet seen any payouts. They know the next big win, or any win is due to pay out. The rush is that if they leave after depositing so much money in the machine it will erupt and the payouts will be often and large. Maybe it can really work if you have already spent thousands of dollars and have got nothing back. The machine will pay any way.
In the old days when a payout occurred players would feel the coins to see if they were hot or cold. If the coins were hot they believed that the machine had not paid for a long period of time. But in reality any machine has numerous lights which heat the coins.
Chaser is the next type of slot players.
The player believes the slot machine is not one of those machines that never pay. The player have won and being reinforced by the win gains trust in the slot machine. One can feel the atmosphere of comfort and trust between the machine and the player.

You can be sure that slot machines are designed to be honest. But there are some manufactures that design the slots in such a way that they can deceive players.
The very first slot machines worked according to the following principle: the wheels spun and then each of them stopped randomly. Modern slots are much different. There is a chip inside of every slot machine, this chip is programmed to select numbers randomly. The selected number determines the symbol which then comes out. 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. Inspectors look at brands of machines and their chips before they are installed in casinos, but they can’t inspect each machine. 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. If you think you’re playing a machine that is not honest, you can complain. In the case if the complaint the inspectors will visir the casino and check whether the machines have a legal chip. Manufacturers that cheat are fined or they can lose their license.