Stay informed with the
Recent Articles
Best of John Robison

# RNG, Hit Frequency, Winning at Slots, Volatility Index

24 August 2003

I am planning on giving a seminar on playing slots to a large group of home owners. I would like to purchase some pictures of certain basic machines to use as visual aids. Can you help me as to where I can acquire these pictures? I did try to download some with the computer, however they were too blurred. I would really like IGT's Blazing 7s, Double Diamonds, Triple Diamonds, Five Times Pay, and River Gambler.

Thank you for your time and response,
Harold

Dear Harold,

Try going to the IGT site (www.igt.com). They have some pictures of machines that you can grab from their site. If those pictures are too blurry, send an e-mail to the webmaster from the Contacts page and ask about getting pictures of machines. IGT is your best source for high quality images.

Also, try searching the Internet for companies that sell slot machines. They usually have pictures of machines on their sites.

John

* * * * * * * * * *

Can you define, in specific terms, the Volatility Index that is referred to by many reviewers of slot games?

What is a desirable value for the Volatility Index to keep a game from being a 'grind' and which gives the players the reward of mid-level prizes on a reasonable frequency to keep them in the game?

Thanks,
Jack

Dear Jack,

The Volatility Index (VI) for a machine is usually based on the 90% confidence interval. You calculate it by multiplying 1.65 times the standard deviation for the paytable. You can find an excellent example of the calculations in Casino Operations Management by Kilby and Fox.

The VI is one way to compare machines based on how many spins it will take for the actual payback on a machine to approach the theoretical payback. The higher the VI, the more spins it will take.

I don't think the VI can be used to answer your question. Let's say there is a payout of X with probability p(X). If we doubled the payout and made the probability of hitting it 1/4 p(X), we would have roughly the same contribution to the standard deviation for both payouts, yet they would have very different playing characteristics. Of course, I'm looking at two payouts in a vacuum. One must really take into account the entire paytable. The doubled payout may have the same contribution to the standard deviation as the non-doubled payout, but it has only half the contribution to the long-term payback of the machine. Other payouts may have to be increased or made more likely to maintain a competitive long-term payback. To change gears completely, maybe the VI can be used in the manner you asked and not just to compare machines in terms of bankroll swings.

I checked my database of slot payback programs and it looks like many popular games (Double Diamond, Triple Diamond) have VIs in the high teens and twenties.

Any article I wrote before the demise of @home.com will have my old @home.com e-mail address in it. There are far too many of them for me to go back and edit them.

John

* * * * * * * * * *

Dear John,

However. in reading a late article about "Buy-A Pay" machines, you indicated that increased coins improved the hit frequency.

If the RNG is selecting the number for the resulting spin and has no part in number of coins played, how can playing increased coins increase the hit frequency, I was under the impression that the RNG selects numbers only without regard to coins played.

What am I missing?

Harold

Dear Harold,

A number produced by the RNG is used to determine which symbols will land on the payline. The probability of any particular symbol landing on the payline is the same regardless of the number of coins played.

The number of coins played comes into play only when it's time to determine whether or not the combination on the payline is a winning combination.

Let's say you're playing a two-coin Blazing 7s. The probability of landing three 7s on the payline is the same regardless of the number of coins you're playing. But three 7s is a winning combination only when you play two coins. The hit frequency is higher when you play two coins, but there's been no change to the RNG formula or the layout of the virtual reels.

Best of luck in and out of the casinos,
John

* * * * * * * * * *

Wow! Here I go again. Hope you don't mind a second question.

Your article on the RNG was great and in detail that I feel I understand it well. How what about something called the SMP? I think this stands for subtract measure percentage?

Do you have information on that as you have for the RNG? I just don't seem to find much about it.

Thanks,
Harold

Dear Harold,

There is a system for betting at the track the uses something called Subtract-Measure-Percentage. The system is supposed to exploit some aspect of the pari-mutuel software that ensures a profit for the track.

I don't know anything about it other than what they say on their website. I can't see any application to slots. I can see that anyone who purchases this system has probably wasted his money.

John

* * * * * * * * * *

When I get the slot's message welcoming me back to a casino, I can't help but wonder that the computer, which knows that I was there not too long ago and that I happened to win a jackpot, won't figure, "Isn't it time to get some of those winnings back?"

Certainly that information is stored in the computer memory banks and can be used very efficiently.

Rick

Dear Rick,

You can relax, Rick.

The probability of hitting anything on a slot machine is determined by the layout of the symbols on the virtual reels in the machine. The only way the casino can change the probability of hitting a winning combination on a machine is to change the chips that contain the layouts of the virtual reels.

There is no way for the Slot Club software to signal a machine that it should try to win back some of the jackpot you hit on your last visit.

Best of luck in and out of the casinos,
John

* * * * * * * * * *

Hi John,

I live in B.C. and I always go to the casino to play the slots. I was just wondering, how can you tell which machines will pay out, and the ones that will give you the jackpot?

I usually put in three quarters at a time, which is the most we can put in. I noticed when I play a machine, after a while, it will stop for a second, and then it will light up the spin button, then I can play again. What is it doing?

How can I win at the slots?

Thank you,
Tam

Dear Tam,

There's no way to know when a machine will pay out or hit the jackpot. They don't give out any kind of signal to let you know.

When a machine takes a short pause, it is updating some accounting information that it has to maintain for the slot regulators. It takes a few seconds for it to update that information.

How can you win at the slots? I know of only two ways to win at the slots. One way is by ensuring that you're only betting money you can afford to lose, playing machines that give you the kind of slot-playing experience that you desire, and using your slot club benefits as much as you can.

The other way to win at the slots is to own the slot machine.

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.

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