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Best of John Robison

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Shocking RNG Answer

22 August 2005

I go to some of the Indian casinos in Washington and I was wondering on the video slots (Beyond the Reef, Texas Tea, Little Green Men, etc.) if stopping individual reels makes a difference? Or as soon as you press the play button your payout is already determined. I usually do fairly well, but I am curious.

Thanks.

Pressing the Stop Spin button has no affect on your outcome. The only thing it does is cut down the length of time that the reels spin.

Best of luck in and out of the casinos,
John


Dear John,

I read your emails on a weekly basis and especially enjoy the ones with humorous replies, for example the response to mathematics and slots where you indicated the earth was flat and the center of the universe... I chuckled about that one for several days.

I do hope I am not setting myself up for a similar response, but here goes...

I understand that the RNG has no memory of previous hits or misses. But, can a particular slot be programmed not to hit under a certain dollar amount? (I am referring to in-house progressive machines and not wide-area progressive machines.)

Thanks for your help.

Sincerely,
Pam

Dear Pam,

I struggled to come up with a snide reply, but I just can't do it when someone asks an intelligent question and appears to be open to the answer -- even when that answer may go against common belief and observation.

The rule in most (if not all) jurisdictions is that if a combination appears on a paytable, it must be possible to land it on every spin. A slot cannot be programmed to not hit its progressive when the progressive is under a certain amount.

Best of luck in and out of the casinos,
John


Hi, John,

Would it be legal/possible for a casino to have different payouts on the same slot machine, depending on how many coins you play? Example: playing 9 lines with 1 credit/line having a higher payout than 9 lines with 5 credits/line.

Thanks for your help,
Donald

Dear Donald,

Absolutely. Machines frequently have different long-term paybacks based on the number of coins played.

But not in the way you implied. You implied that the machine would switch to a better-paying reel layout because the player upped the number of coins bet per line.

The only ways a machine can have different long-term paybacks based on the number of coins bet is by 1) activating additional winning combination (e.g., Buy-a-Pay machines), or 2) paying a bonus on one or more winning combinations (Bonus Multipliers).

Best of luck in and out of the casinos,
John


John:

I was reading your answer to how the RNG works in a slot machine. Your answer was very close to correct, except that the EGM seeds the RNG based upon input (button press, touch screen touch) from the player. This would seem to imply the player can affect play, however the player has no way of knowing where they are in the universe of RNG cycles nor can they physically hit the button in time to affect play.

This e-mail came from someone who works at one of the major slot manufacturers. EGM stands for electronic gaming machine and is regulator-speak for slot machines, video poker machines, etc.

I've written many explanations of the RNG in the years I've been answering questions online and because each answer is tailored to the questioner, no single answer is ever complete. I think I have only mentioned reseeding the RNG in discussions of RNG cheats -- for the exact reason that this writer gives. It seems that players have some control over their fates, but they don't.

I have the same problem trying to explain that while it's true that players will have different outcomes on a spin based on the number of coins they play or whether they pull the handle or press the Spin button because the game is initiated at different times, but the different outcomes are not going to be any better or worse than any other set of outcomes in the long run./p>

I think I finally found a way to illustrate this. Consider throwing two dice, one red and one green. Over the long run, the two dice are going to show the same characteristics, even though the numbers rolled on any given roll may be different.

Thanks for providing more insight into the workings of the RNG.

John


John,

Your response to the question about when the random number generator selects your result --

"In fact, most machines today operate this way: After you hit the Spin button or pull the handle, the program polls the RNG to get a random number to determine the symbol for the first reel. The program then polls the RNG to get the number for the second reel, and then polls the RNG one more time to get the number for the third reel. I don't know whether the program waits until after it stops one reel before it gets the number for the next reel or gets all the numbers and then stops the reels -- in any case, that point is irrelevant."

really shocked me. Three polls - one for each reel - seems illogical. Most everything else I've read on this topic recently says there's only one poll - regardless of the number of reels, or whether the machine is a video slot or not.

From a "universe" of, say, 90,000,000 or whatever for a linked machine with a large jackpot, I've been led to believe that a single number -- like 13,027,426 -- gets selected, and that single number already is programmed with the corresponding "stop" points on all the reels (or video equivalents). And, by the way, if that combination of "stop" points happens to be a loser or a minor winner, you can be sure that hundreds or thousands of other numbers in that 90 million number universe have been programmed with exactly the same "stop" points.

Conversely, if the random number selected happens to correspond to a major jackpot, very few (and maybe no other) random numbers selected form the universe contain the same "stop" point as those for the big winners.

Can you get a re-confirmation of the separate-random#-selection-per-reel method from one of your inside information sources?

Joe

Dear Joe,

First off, you have to be careful with comparing conceptual descriptions given to non-programmers with actual algorithms used within the machines. Most non-technical slot writers use the "numbers assigned to different combinations" description of how the RNG is used to select the outcome. I've always used a more algorithmic approach.

Why is it illogical to poll the RNG separately for each reel? I think it's a little easier than using just one number, but it's really irrelevant whether the machine uses one poll for each reel or one poll total to determine the result.

Let's take a look at what actually happens when the machine needs to determine the outcome of a spin. The program polls the RNG to get a number. There's no lookup table that says a particular number corresponds to a particular combination. Instead, there are virtual reel tables. The machine needs to take the number it got from the RNG to select virtual stops on the virtual reels.

The program could factor this number to get a separate number for each reel or it could use separate polls of the RNG for each reel. That doesn't matter. What does matter is that the program does something to the number to get it in the range of the number of virtual stops on the virtual reel (probably modulo arithmetic) and then that number is used to select the virtual stop.

Each virtual stop points to a physical stop on the physical reel. By looking at the symbol at the physical stop pointed to by the virtual stop, the program knows which symbol will land on the payline.

Now, if the program does use only one poll, you could work in reverse and "un-factor" individual reel results into the number that lead to them and figure out all the numbers that lead to a particual symbol combination. You could then say that those numbers are assigned to that particular combination.

But given the description of how things actually work that I gave, you can see that the "numbers-assigned-to-combinations" does not accurately describe how the machines work.

My statement that most machines choose separate numbers for each reel is based on a recent communication with a manufacturer. I'm not sure, but it may also be the current regulation in Nevada.

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 send a reply to every question. Also be advised that it may take several months for your question to appear in my column.

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