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Best of John Robison

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Ask the Slot Expert: Misperceptions about the RNG

26 June 2013

If events are random, controlled by the RNG, why is it when I miss a pay I can get the same losing results often (for example, single bar--blank--single bar, or something along those lines). Many times I get the same results twice in a row. Could it be I hit the button the exact time so many times?

I realize there may be more numbers in the RNG that coincide with that combo, but if so I'd say many numbers because I see certain combos often. Unfortunately they are losing combos -- lol.

I am puzzled by this because, if truly random, why would these come up so often?

Enjoy the columns as always.

Thanks,
Mike

Dear Mike,

Thanks for the kind words.

Yes, there are many more numbers in the RNG that correspond to losing combinations than winning combinations.

You know, I really don't like trying to "simplify" what happens in a slot machine with this statement that "numbers in the RNG correspond to symbols." Although it is essentially true, the description leads to misperceptions, like RNGs can be tight or loose. What actually happens in the machine is reasonably straightforward.

After you start a spin, the machine has to figure out where to stop the reels. To do this, it gets a number from the RNG. That number tells the machine where to stop the reel, but not directly. The reel inside the machine has 22 positions on which it can stop. These positions are called, logically enough, stops. In order to pay five-figure and larger jackpots, the jackpot symbol has to be less likely to land on the payline than 1 out of 22 on each reel. So the machine uses an intermediate table (called the virtual reel table) to pretend that the reels have 32 or more stops on them. Each stop on the physical reel appears one or more times on the virtual reel. The jackpot symbol appears many fewer times than the single bar and blank symbols.

The number from the RNG is actually used to select a virtual stop. The virtual reel table then tells the machine which physical stop and symbol should land on the payline.

So, let's go over the process of selecting the results of a spin the way it really happens.

After you start a spin, the machine has to determine where to stop each reel. It gets a number from the RNG. It uses this number to select a virtual stop from the virtual reel table. The entry in the virtual reel table tells the machine which physical stop and symbol should land on the payline. That takes care of the first reel. The machine then repeats the process for each reel in the machine.

Numbers from the RNG don't really correspond to symbols. They correspond to virtual stops. The virtual reel table can have different layouts for each reel and it almost always does. The number 14,274 may correspond to a triple bar on the first reel, a single bar on the second, and a blank on the third. In fact, in most virtual reel tables, blanks are more likely to land on the payline on the third reel than on the first two reels. Slot designers put in this imbalance because, on most machines, the game is over once a blank lands on the payline. If you get symbols on the first two reels, you're still in the game.

Let's look at all the different ways you can get a single bar with different numbers from the RNG. First, the single bar appears multiple times on the physical reel. You may have gotten the single bar on the first reel on two spins in a row, but each one might been a different physical stop on the reel. Each physical stop would be a different number from the RNG. If the single bar symbols appears twice on the physical, we have two different numbers that give identical results on the payline.

Second, let's bring in the virtual reel table. The single bar symbol undoubtedly appears many times in the table, each virtual stop corresponding to a different number from the RNG. If the single bars appear 22 times in the virtual reel table, we now have 22 different numbers that yield the same result.

Now, let me throw a curveball. The numbers from the RNG fall in a very wide range -- from 0 to over 2 billion. The numbers have to be scaled down so they fall in the range of the number of virtual stops on a reel. This mathematical process is known as modulo (or clock or remainder) arithmetic. Simply put, if you divide and number no matter how large by, say, 32 and take the remainder, the remainder will be a number from 0 to 31. There could be millions or tens of millions of numbers from the RNG that lead to that single bar after being scaled.

Landing the same symbols on the payline two spins in a row does not mean you got the same numbers from the RNG twice in a row. There are many ways to get to identical results.

Jackpots for all,
John


John Robison

John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots
John Robison
John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots