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Best of John Robison

Gaming Guru

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Am I wrong about how slot machines work?

28 May 2007

John,

As a retired programmer (and systems analyst) I got interested in the programming of slot machines shortly after I retired. I learned a lot, and thought I had a pretty good grasp of how the modern slot machines were programmed to exhibit a specific payout percentage over the long term. I've even developed my own pseudo slot machines with virtual reel tables and specific payout percentages.

The other day while visiting a nearby casino, I saw (and experienced) a phenomenon for which I really don't have a logical explanation.

For several weeks now, I've been keeping my eye on a particular bank of new machines that were installed in the casino where I visit. Just from observing others playing a couple of the machines in this bank of eight, I decided that two of them were very likely set to a high percentage payout than the other six. Just recently, I went over for lunch and decided to play one of these two machines. Before lunch, I noticed a grey-haired lady playing the machine I would like to have played. This machine is not a video representation of spinning reels, but does have actual reels. It is a 5-reel machine and the player can play at most nine lines, and they can play multiple coins per line. This lady was always playing two coins per line and played all nine lines. I watched her for a little while before lunch, and her credits amounted to roughly $25. As I observed her play I noticed there were "downs" she would experience, but then there would be an "up" that would recover the previous loss and would actually bring the credits up slightly above the $25 mark that I had first seen her playing at.

I thought surely she would get up and leave, but she didn't. I went to lunch and was only gone about 40 minutes. When I returned, the same lady was sitting at the machine and was playing it the same way. Only now she had credits that amounted to about $34. I was determined to play that machine, so I lurked around behind her for a long time, all the while observing where the credits were going. As before, there would be some "downs" and then an "up" that would give her a slight gain. After watching her and not playing myself, I got bored and decided I could not outlast her. But I watched this same lady for a little over 3.5 hours (and that's a lot of spins), and when I finally left, her credits were up to about $75. I have no idea what happened after that, but I made a vow to come back another day and play that machine. Now, mind you, this was not the first time I've observed this machine exhibit this sort of "return characteristics".

I'm guessing the virtual reel table could really have at least 64 stops, and it might have 128. If it's 64, then there are a possible 1,073,741,824 different combinations that could be displayed. And, that might be the odds for winning the Jackpot. If it's 128, then there are a possible 34,359,738,368. Not once, in all the time I've spent observing this bank of machines (and specifically these two) have I ever seen a player hit a Jackpot win, or even something close to a Jackpot win.

Anyway, the very next day, I returned to the casino and found no one playing this particular machine. I slipped in a $20, and played the same two coins per each of the nine lines. What happened next has me completely dumbfounded, and seriously doubting that I really understand much at all about the internal programming of a slot machine. It was like I was sitting at a totally different machine from what I'd observed just the day before. The machine had it's usual "downs", but the subsequent "up" only barely brought me back to where I had started, and after about an hour of play, I'd experienced several "ups" and "downs", but my original stake of $20 was now definitely on the decline, and not on an incline, like I'd observed just the day before. I imagined I was just seeing some anomaly or fluke of the pseudo random number generator, so decided to ride out the anomaly. I was certain the machine, would return to the same "characteristics" I'd observed just the day before, for a 3.5 hour stretch. After my 3 hour stretch, I had basically lost the entire $20, and was really confounded.

During my initial investigation of slot machine programming, I was told by an agent that works at the Gaming Labs in PA that tests slot machines, "...that it is not possible to change the payout percentage of a slot from a central computer, but in fact it required a chip change within the slot, and a great deal of paper work...". Further, I was told that it is unlawful to be able to change the payout characteristics of a slot machine from a remote, centrally located computer. And, I believed those statements.

So, my question is this: Are my beliefs about slot machines not being able to have their payout characteristics changed from a remote computer WRONG? Further, if the payout characteristics were not changed, what is the logical explanation for what I observed in a 3.5 hour period of time on one day, and then observe a completely different characteristic on the following day?

I'd like not to have to wait for my answer to appear in your written column. Is it possible you could just give me a reasonable (believable) explanation for what I just experienced?

Thanks a lot,
Sam

Dear Sam,

First, the machine you were watching may or may not have used virtual reels. Virtual reel technology is used to lengthen the odds on slots without adding additional physical stops on the reels or additional reels. Because those machines have five reels, they may not need to use virtual reels. Five reels with 22 stops each gives 5,153,632 possible outcomes. There's no way to know for sure whether virtual reels are used without seeing the par sheets for the games.

Second, you have to be very careful about drawing conclusions about machines with limited observation. You may have six to seven hours of observation and playing the machine, but you've experienced only about 3,000 spins. Consider two nearly identical machines. One's long-term payback is two percentage points lower than the others. It typically takes tens of thousands — if not hundreds of thousands — of spins for a change in payback to have a greater effect than randomness on the payback you experience while playing a machine. In short, you don't have enough observations to draw a conclusion.

I'm not surprised you didn't see a jackpot hit in "all the time you spent observing this bank of machines." Without the par sheet, we don't know the mean number of spins between jackpot hits. Just as an example, video poker machines hit royal flushes about once every 40,000 hands, on the average. I estimate that you saw only about 24,000 spins during the time you were at the bank of machines. And that's assuming that all eight machines were played for eight hours at six spins per minute.

The agent you spoke with is correct. Most jurisdictions require chip changes to change the long-term payback on a machine. A few casinos are testing downloadable games, but none of them are in Pennsylvania.

The logical explanation for what you experienced is randomness. I and many others have seen banks of machines hot one evening and then ice cold the next time we played them. Nothing was changed on them machines. The different experiences were a result of 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 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