How coin machines work

how coin machines work

Slot machines are random

Slot machines work like every other casino game:

  1. In every round there's a random result (from dice being thrown, cards being dealt, or reels being spun).
  2. When you win, the payout is less than the odds of winning.
In other words, the casino has a built-in mathematical edge on the games. The casino doesn't have to screw with the dice to beat players at craps, they don't have to screw with the cards to beat players at blackjack, and they don't have to screw with the machines to beat the players at slots. The payline symbols are chosen at random, and it's the math that ensures that you're a long-term loser.

As humans we try to look for patterns. We "sense" that the machines run in hot or cold cycles, that they pay better (or worse) at different times of day, or that other various things influence the results—but they don't. We look for patterns because we're not comfortable with cold, hard, non-patterned randomness. But whether you like it or not, random results is what you get.

That means, for example, that it doesn't matter how long it's been since a jackpot hit. The odds are the same on every spin. You've got the same chance of scoring a jackpot on a machine that just hit one, as a machine that last hit one three months ago. A machine is never "due" to hit. Every spin is random. The random nature of slots also means that it's impossible to predict when the payouts will be good. Any streaks you see are pure chance, nothing more.

That makes sense, because the whole foundation of casino gaming is randomness. Every other game in the casino, from craps to roulette, works the same way. The outcome is random, and the odds are simply tilted in the casino's favor. There's no mystery about slots, just like there's no mystery about craps. Why would there be?

Even if the casinos wanted the machines to operate otherwise, they don't have a choice. Gaming regulations demand that the machines are completely random. For example, this is from Nevada Gaming Regulation 14 (PDF):

"[A gaming device] must use a random selection process to determine the game outcome of each play of a game. Each possible permutation or combination of game elements which produce winning or losing game outcomes must be available for random selection at the initiation of each play. The selection process must not produce detectable patterns of game elements or detectable dependency upon any previous game outcome, the amount wagered, or upon the style or method of play."

There you have it. Slots aren't affected by the presence (or absence) of a player's card, how long it's been since the last jackpot hit, or anything else. Slots don't have periods where they pay out more to "make up" for earlier periods where they paid out less. They're random, period. Anyone who says otherwise is simply pulling B.S. out of thin air and declaring it to be fact, with no evidence to support their delusions.

The Simplest Slot Machine

To prep us for understanding the odds on slots, let's start with something simple: a coin-flip game. You bet $1 on the flip of a coin. For every heads you win $1, and for every tails you lose $1.

It's pretty easy to see that this is an even-sum game. You would expect to be dead-even in the long term. Which is why the casino would never offer such a game—there's no profit in it for them. So now let's modify the game, to give the casino an edge. In the casino version, you still lose your dollar when you get tails, but when you get heads, the dealer pays you only 90ў.

You don't have

to be a rocket scientist to see that the casino has an edge on this game. It's a long-term loser to the player. The average loss is 5ў per bet: for every dollar bet on average, the player will get back 95ў, and the casino will keep 5ў as its profit. (If you thought the average loss was 10ў, remember that the penalty kicks in only when you lose, which is only 50% of the time.)

By the way, if you think it would be crazy to play such a losing game, then ask yourself why people gamble in the first place, because casino games are the same kind of sure losers as our coin-flip game. In fact, many casino games are even worse: the house edge in roulette is 5.3%, and on most slots it's even higher.

Anyway, back to the coin-flip game. Okay, so now let's say that the casino wants to turn the game into a machine version so they don't have to pay a dealer to stand there all day and flip a coin. The design of the machine game is pretty easy: We program the machine to choose a 0 or 1 randomly, to show a spinning coin, to stop on heads when it picked 0 and to show a tails when it picked 1, and to pay you 90ў when you got a heads.

We can even make it work even more like a slot machine: Instead of a spinning coin, it's a slot machine with a single reel. with 11 heads symbols and 11 tails symbols.

Anyway, from this example you can see that all the casino needs to do to win is to provide a random game. There's no need to program in streaks or cycles or anything else. As long as the game is random, the player will be a long-term loser.

Slot machines work exactly same way: The payouts are simply less than the odds of hitting them. You can't beat a coin-flip game when you're paid only 90ў on your wins. By the same token, you can't beat a slot machine since it underpays you on your wins.

Picking the symbols

Enough coin-flipping, let's move on to slots. On a slot machine, a random number generator (RNG) picks a random number for each reel, which each number picked corresponding to a stop on its reel. Then the machine directs the reels to stop on the spots selected by the RNG.

Note that by the time the reels are spinning, the game is already over. The RNG has already selected the stops, and the reels spin sort of as a courtesy to the player. Slot machines don't even need visible reels—you could just put your money in and the machine could tell you whether you how much (if any) you won. Wrap your head around that one for a minute. The presence of the visible reels makes no difference in the game—they're just there to show you what the computer picked.

How the stops are selected

If you saw a worker open up an electro-mechanical slot machine you might see a reel like the one on the right. if it were unfolded. There are various symbols spread across 22 stops. Yes, the blanks count as stops. You might think that since there are 11 blanks you have a 50% chance of hitting one, and since there's only one jackpot symbol you have a 1-in-22 chance of getting it. But it doesn't work that way, because we're not really working with a 22-stop reel. We're really working with an invisible reel of like 128 or so stops, controlled by the computer. The computer will pick a number from 1-128, each of which is mapped to a specific symbol. Here's a hypothetical map for the reel shown at right:


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