Random Number Generator
There are many modern computerized slot machines. 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 are chosen by 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. The most recent random number is used to determine the result when the Play button is pressed. The result varies depending on exactly when the game is played. The result changes every fraction of a second.
Some professional gamblers observe that the RNG does not actually generate random numbers. The sequence of numbers is repeated by most of the RNGs. Poor programming is its reason. Pseudo RNGs with very long periods canbe built relatively easily. The computer that is able to complete a single period in the expected lifetime of the universe hasn't been invented yet. It was Ronald Dale Harris, a former slot machine programmer, who knew the pseudo RNG code and seed values. He 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. 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.

Payout Percentage
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. The minimum theoretical payout percentage varies among jurisdictions. Its establishment refers to the sphere of 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 main criterion for selecting the winning patterns on slot machines is that they should yield a certain fraction of the money played to the house. The rest of the money goes to the players.
A slot machine's software is written and the theoretical payout percentage is set simultaneously. To change the payout percentage after a slot machine has been placed on the gaming floor a physical swap of the software is required. Being a time-consuming process it is done not very often. In certain jurisdictions the EPROM has a tamper-evident seal. 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.
The Nevada Gaming Commission is working now with Las Vegas casinos on technology that 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 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. A small amount is contributed by each machine in the group to this progressive jackpot which is given 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.
There can also be multiple casinos consisting of multiple machines. In these cases the manufacturer owning these machines is responsible for paying the jackpot.

Near-miss
The reel display of modern slot machines is under computer software's control. Combinations that are close to winning combinations can be displayed on the slot machine intentionally.
This practice of 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. Winning percentages programmed into the slot machine control the chance of a winning combination appearing on a pay line. The combinations above and below the payline 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, virtual reels are used and 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. They ruled that this was legal, so 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. 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. Stop motion cameras are used by regulators for manufacturer's practices audit.

Slot Machines Fraud
Sometimes mechanical slot machines and their coin acceptors seem to belong to cheating devices and other scams.
EPROM computer chips controls modern slot machines 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. One of the recent attempts at defrauding slot machines 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 you'll spot a winning slot machine is when the bells are ringing and the money is dropping. RNG is the main element of every slot machine and one never knows what combination it will form.
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.
It is not so. With every game the chances of winning are the same.
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.

United States
In the United States the availability of slot machines is regulated by governments. There are a lot of states that have established gaming control boards to regulate the possession and use of slot machines. There is only one state that has no significant restrictions against slot machines - Nevada. Slot machines are allowed only in hotel casinos operated in Atlantic City in New Jersey. In some states slot machines are allowed only on licensed riverboats or permanently-anchored barges. In Delaware there are slot machines only at three horse tracks. They are regulated by the state lottery commission.

Native American Casinos
Slot machines are forbidden in Native American casinos located in reservations. It is permitted when the tribe first reaches a pact with the state in which it is located. Typically, a pact entitles the state to receive a fraction of the gross revenue from slot machines.

Classes Of Slots
No federal law governs slot machines. Each state has its own classification. There are restrictions on the type of slot machines that can be used in a casino or other gaming area in some states. The operation of "Class III" (or "traditional") slot machines is fulfilled from a centralized computer system. The chance of winning any payout is the same with every play. Nevada or Atlantic City have more Class III slots than any other state. "Vegas-style slots" is another name for them.
There is a connection between "Class II" slot machines ("video lottery terminals" or "VLTs") and a centralized computer system. It determines the outcome of each wager. The chance of winning a series of limited prizes is equal for each machine. The casino pays a fee to the state for each Class III game. The state doesn't regulate Class II games so tightly.

Characteristics Of Class II Games
The players are playing against each other. The prize is common. One player always wins the game. The game is continued until someone wins. There is a certain number of wins and losses in a given set of wins. The combimation that has already occurred cannot occur again until a new batch is initiated. The games are dependant on each other. The player is an active participant of the game. The same set of numbers is played by all players.

Class III Game Characteristics
The player is playing against the house. The previous games don't influence the following ones. Any possible outcome can occur in any game.

Clubs Of Slot Players
Free memberships in "slot clubs" is offered by many American casinos. They offer to return a small fraction of the amount of money that is bet in the form of comps. The cards are used to insert into the slot machines in these clubs. Comps or "cash back" from these clubs can make significant differences in the maximum theoretical returns.

Australia
One of the most popular Australian poker machine games is Queen of the Nile. Gaming Machines is an official name for Australian slot machines. Physical reels are stimulated by video displays in Australian-style gaming machines. There are five of them in most cases. State governments regulate the use of gaming machines in Australia.
Not only casinos but also pubs and clubs in some states have Gaming machines. New South Wales was the first state to legalize this style of gambling. The year of 1956 was the year of their legalization in all registered clubs in the state.
The usage of particular forms of gaming machine is allowed in Western Australia.

United Kingdom
The terms fruit machines, one-armed bandits and AWP are used to denote slot machines in Britain. Fruit machines are commonly found in pubs, clubs, arcades, and some take-away food shops. There can be 3, 4 or 6 reels with around 16 or 24 fruit symbols printed around them. These reels should be spun. If certain combinations of fruit appear, winnings are paid from the machine. There is similarity between these machines and slot machines seen in casinos and elsewhere around the world. These games have lots of extra features. However, the jackpots from these fruit machines are strictly limited. The UK fruit machines have some features. A player may be given the opportunity to hold one or more reels before spinning. This can sometimes increase the chance of winning. A finite number nudges following a spin is given to a player. A nudge is a single-step rotation of a reel of the player's choice.
The maximum payout for an individual game is influenced by the type and the location of the machine. Private members' clubs are allowed "club machines". They have higher jackpots and are allowed to charge more per game.
These machines also operate in a different manner to American slot machines. The jackpot can be won in each game independently.
The AWP fruit machine is popular across Europe and in countries such as the Czech Republic, Russia, and Ukraine.

Japanese Slots
Pachisuro is the name for Japanese slot machines. Their ancestor is the traditional Japanese pachinko game. Slot machines are new phenomenon. There are slot machines in pachinko parlors and the adult sections of amusement arcades, known as game centers.
The machines are regulated with IC chips. They have six different levels changing the odds of a "777". All machine varieties have certain rules and regulations.