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Best of John Robison

Gaming Guru

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More on the RNG

12 July 2004

Dear Sir,

My wife and I live very close to an Indian gamming facility in California. It's an isolated casino, so the payouts seem to be very low. However, it seems that when we donate our service to the local resevation's "people needs", our payout frequency seems to spike sharply. I was wondering what your thoughts were on this hit frequency payout ratio.

Sincerely,
Jeffrey

Dear Jeffrey,

I think it's just a coincidence or a misperception that your hit frequency increases after you make a donation.

Best of luck in and out of the casinos,
John


Hi, John:

I read your columns regularly, and I've noticed that slot players have become very interested with the operation of the RNG. I also have some questions related to the RNG:

How long does it take for a machine (the RNG) to cycle through all the possible combinations that a machine can generate?

If I play from accumulated credits, using the max play button, when does the machine make its selection from the RNG?

Is there a way to determine the average number of spins between jackpots on a Double Diamond slot machine? Also if the RNG is totally random, why don't the jackpot symbols line up more frequently?

Are slot machine payout statistics made available to the public (i.e., will a casino tell a customer how long ago a machine hit for the jackpot, and how often it hits over a period of time)?

bobC

Dear bobC,

Slot manufacturers are very reluctant to discuss the technical details of how their RNGs operate.

Let's say a machine generates 100 random numbers per second. IGT's RNG has a period of about 4,000,000,000 numbers, so it would take about 46,296 days for the RNG to repeat. That's assuming that numbers are generated at a constant rate and that the RNG is not reseeded during the run. Both assumptions are faulty. Current machines will vary the pace at which they generate numbers and also reseed the RNG to make it more difficult to cheat the machine by using knowledge of the RNG formula.

Current machines will lock in the result of a spin at the last possible moment before revealing it. The selection is done right after you pull the handle or hit the Spin or Bet Max button.

One way to determine the average number of spins between jackpots on a machine is to watch it for a long time, keeping track of the number of spins and the number of times a jackpot hit. Another way is to look at the machines Par Sheet. Another way is to play a few thousand spins on the machine, counting the number of times the jackpot symbol appears on each reel. This will give you an estimate of the probability of landing the jackpot symbol on each reel. Multiply the probabilities together to get the probability of hitting the jackpot. Take the reciprocal to get the average number of pulls between hits.

The jackpot symbols line up with the frequency determined by the number of times they appear on the virtual reels. What's random is which combination will appear next. What isn't random is the frequency with which those combination will appear.

Many casinos will put signs over their high-paying machines. That's useful information. One casino (in the Chicago area, I think) used to hand out a list of machines that have recently hit jackpots or some such nonsense. This "gossip" doesn't provide anything useful because the odds are the same on every spin.

You can find out a machine's hit frequency just by playing it. Play 1,000 or more spins and note the number of hits you get. That will give you a pretty good estimate of the machine's hit frequency.

Best of luck in and out of the casinos,
John


Great column. STYW stands for Spin 'Til You Win.

Thanks for the good information you give.

Karen

Dear Karen,

Thanks for the kind words and thanks for clearing up the mystery about that abbreviation. (A past column contained a letter from someone asking about slot terms and abbreviations and that one had me stumped.)

Shame on me for not realizing what STYW stood for--but honestly I've never seen it on a sell sheet or in other manufacturer literature--because I had a very enjoyable session on a machine with the Spin 'Til You Win feature at The Mirage a few years ago. The Mirage had a bank of machines from Anchor Gaming and I had the Par Sheets for those games. I wanted to test my theory that you could estimate the probability of landing a particular symbol on the payline by counting the number of times it appears. Well, that's not a theory, it's a fact. The trick is in playing a sufficient number of spins to get a decent estimate.

In any case, I was playing this machine and noting which symbols appeared on the payline. I was wearing a Mirage logo shirt and many people, even some employees, though I worked for the casino. This machine was hot. Red hot. Hotter than hot. They had to fill the hopper twice while I was playing it. I had to have a slot host help me carry the buckets of coins over to the coin redemption booth.

Hot sessions. I just love it when they happen. Too bad they happen so infrequently.

Best of luck in and out of the casinos,
John


I love your newsletter.

I recently returned from a vacation in Las Vegas and Laughlin. I searched for some of my favorite penny machines that my favorite Casino in Arizona has and could not find them anywhere. The machines are made in Australia; do Nevada casinos have only American-made slots?

Have a day filled with blessings.

Thanks for the kind words.

Nevada casinos have slots made in many countries, including Australia. Aristocrat, the big manufacturer from down under, has machines in many casinos, but maybe not in the ones you visited. My impression is that their non-branded machines are most frequently found in locals casinos, while their branded games can be found in both locals and strip casinos.

Best of luck in and out of the casinos,
John


Between casino visits, I play Masque slots on my computer. I enjoy the IGT machines the best. How close is this to an actual casino experience? RNG?

Thanks,
Ray

Dear Ray,

You tell me. How close is playing on your computer to playing in a casino? How many times does the cocktail waitress come by your computer? Does your computer ever comp you for a buffet? Can you press the Cash Out button to collect your winnings?

Seriously, some of the machines have slightly different rules as compared with their casino counterparts. I don't know about the paybacks on the PC games, but they could be much higher than those on the real slots. The RNG may not be as sophisticated as the one in the real slot, but I'm sure it satisfies sufficiently the tests for randomness.

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 two or more 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