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# More on the RNG

25 January 2010

John,

Thanks for the info on the RNG. That helps out quite a bit but leaves me to question as to how random the results actually are. If the system uses the last calculated value and generates a number from it wouldn't the results follow some sort of sequence over time? I do realize that unless you're "Rain Man" you would never be able to memorize the sequence, nor would you able to stop the reels at exact intervals to follow the pattern. But I often wonder if computers are able to truly generate random numbers.

I say this because quite often, I get the "teaser" spins frequently on machines only just before and after a good payout, and only occasionally when they are not paying (that sentence is hard to follow I don't know how to restate it). I do admit that sometimes I am surprised and the results are not what I expect at all.

In your last paragraph you say that the RNG is polled individually for each reel. If the result of the first poll helps to calculate the second poll and so on then in the case of say the number 100,000 is pulled from the RNG on consecutive spins then the results on all three reels would be the same for consecutive spins? If that's true wouldn't it be simpler to use a table that has the results for 1-262,144 and the symbols appear accordingly?

Thanks for your help,
Kris

Dear Kris,

The RNG in a slot machine is more correctly called a pseudo-RNG. The number stream it generates is not truly random, but it satisfies many of the tests for randomness. There is a sequence to the numbers. Even if you could memorize the sequence, you wouldn't be able to start a game when the RNG has a particular value because the machine is generating numbers much faster than human reaction time.

I'm not surprised that sometimes the results are not what you expect. After all, the results are random -- or at least as close to random as it can get on a slot.

The software in a slot machine could use a table instead of an RNG function. Even though memory is getting cheaper every day, why use hundreds of thousands of memory locations to store a table when an RNG function requires only a few hundred or thousand locations?

Best of luck in and out of the casinos,
John

Send your slot and video poker questions to John Robison, Slot Expert, at slotexpert@comcast.net. Because of the volume of mail I receive, I regret that I can't reply to every question.

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