Generator Of Random Numbers
Nowadays slot machines are computerized. They programme the odds. The reels and lever are present for historical and entertainment reasons only. A Random Number Generator determines the positions of the reels. The machine's software includes a Random Number Generator.
The RNG generates random numbers at an extremely high rate. When a player presses the Play button the most recent random number determines 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.
It was noticed that the RNG does not actually generate random numbers. The sequence of numbers is repeated by most of the RNGs. 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. 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 even if nobody uses the machine the RNG continues to pick numbers. So the player cannot see the secquence.

Payout Percentage
Slot machines usually pay out as winnings 82–98 per cent of the money that is wagered by players. This payout percentage is called theoretical. 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. The amounts they pay and the frequencies of these pay-outs are reflected in it. 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. The rest of the money goes to the players.
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. In certain jurisdictions the EPROM has a tamper-evident seal. Gaming Control Board officials should be called for changing it. Other jurisdictions constantly ensure that slot machines 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. Only after the selected machine has been idle for at least four minutes can the change be done. After making the change the machine is locked to new players for four minutes, it displays an on-screen message informing potential players that a change is being made.

Machines That Are Linked
Linking the machines in a special way is made to offer a particularly large prize, or jackpot. 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. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own.
Multiple machines can be sometimes 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
Computer software controls the reel display of modern slot machines. 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. Winning percentages programmed into the slot machine 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. The occurance of this phenomenon is possible when 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. 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.
Australia also forbids to use near-miss programming, where a near miss is inaccurately displayed. To audit manufacturer's practices regulators use stop motion cameras.

Fraud
Sometimes mechanical slot machines and their coin acceptors seem to belong to cheating devices and other scams.
Modern slot machines are controlled by EPROM computer chips and 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. An example of modern ways of slot machine defrauding is directing microwaves toward it to disrupt its proper functioning.

As you know there are different types of slot machines. And do you know that there are even types of slot palyers.
Persistent player.
These players are sure that the machine is already ready to pay out, they just have to wait for a little. The machine can begin paying in any second.
The player will play until the machine pays out. He must have found a machine that haven’t paid for a long period of time or he has inserted to many coins and has got nothing. 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. Makes sense if you have lost 0. 00 and have yet to win. The machine can’t but paying.
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. In fact the coins could be hot only because of the numerous lights that heated the coins.
The second type of slot players is a chaser.
The player thinks that the machine he is going to play is not a machine that never pays. The player have won and being reinforced by the win gains trust in the slot machine. There is some kind of comfort and trust between the slot 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 slot machines differ form the old ones greatly. These machines contain computer chips that are 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. That is, inspectors make sure that the machine pays off at the legal rate or better.
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. Some dishonest manufactures use the right to produce machines, but use a different chip, which is programmed to pay less or not so often.
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 effect was two-fold: the machine didn’t pay off, and customers continued to play the machine, thinking that they were very close to a big jackpot. 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.