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Best of John Robison

Gaming Guru

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Ask the Slot Expert: Am I wasting money betting the max on a slot machine?

22 June 2016

Question: Last week you wrote that "the output from the RNG is used to determine where the reels stop."

Wouldn't it be more accurate to say the RNG sends its numbers to the virtual reel, and that determines where the reels stop?

Have read you for years and have never seen you mention virtual reels chip.

Answer: I made that statement about the virtual reels chip last week answering a letter from someone who was concerned that there was a computer chip in the slot machines he plays. If you were to open up the area where the brains of the slot machine are housed (usually called the Logic Drawer), you'd see many chips. I listed many of the different types of chips that a computer system -- which is what a modern slot machine is -- can contain.

The layout of the symbols on the reels has to be stored somewhere in the components that make up the computer system that is the slot machine. The layout should be stored in some component that is non-volatile and immutable, like a ROM (read-only memory) chip or CD, to prevent tampering with the data. Different reel layouts make it possible to have multiple long-term payback percentages for a slot game without changing the paytable.

Turning to your question, I don't think it would be more accurate to describe how the program running the slot machine determines where to stop the reels using your description. It implies that there's some intelligence in the virtual reel layout when, in fact, it's just a table and that the RNG does more than just generate a stream of numbers.

Let's do a high-level overview of how the program running the slot machine handles a spin. Let's assume that the machine has just finished paying off a winning combination and is preparing for the next spin.

  • Check the credit meter. If there are credits left, enable the appropriate bet buttons.
  • Wait for player to press a bet button.
  • React to bet button. Deduct credits bet from the credit meter. Display credits bet in credits played area.
  • Start spinning reels.
  • Get the most recently generated number from the RNG (called Polling the RNG) to determine where to stop the first reel. Scale the number from the RNG to the number of stops on the reel using modulo arithmetic. If this is a reel-spinning slot machine, use the scaled number as an index into the virtual reel layout table to find out the physical reel stop mapped to the number. If this a video slot, the scaled number is the number of the stop. In either case, stop the reel at the chosen location.
  • Repeat the above step for each reel on the machine.
  • Check the physical reel layout table to determine the symbol(s) that landed on the payline(s). If this is a video slot that is not mimicking a reel-spinning slot, there is only one reel layout table.
  • Evaluate the symbols on each payline. Check the paytable to see if any are winning combinations and, if so, add the appropriate amounts to the win and credit meters. This is the only time that the program cares about how much was bet.
  • Go back to the start.

The key difference is that the program running the slot machine calls all the shots.


Question: On the multi-denomination Novomatic slots here in the UK, it states that the average payout is 92%. These machines have bets of 50p, £1, £2, £3, £4 and £5 and 15 different slot titles from which to choose.

Am I right in assuming that incresing the bet increases the average percentage payout? That is, if I bet £5 per spin the average payout is, say, 97% and if I bet 50p the average payout is 87% giving an average of 92%.

If this assumption is right, how come? The PRNG (Psuedo-Random Number Generator) runs all the time and does not know what bet you are making.

Are we wasting out money by betting £5 as the slots are just straight multipliers of the bet with no extra reels or jackpots for increased bets?

Answer: You called these multi-denomination slots, but are you really changing the value of one credit or are you just betting more credits per spin?

If you are changing the value of a credit, it's possible that the higher denominations have more generous reel layouts. We can see that in the United States on video poker machines on which the paytable changes for the higher denominations. Unfortunately, there's no way to tell if the reel layout changes when you change denominations on a slot machine.

Because you called the different bets betting options, I think you're just betting more and not changing the denomination. It's still possible for the machine to give the players who bet more a higher long-term payback without changing the reel layouts or the reeel stopping positions dictated by the RNG, which would be illegal in the U.S..

One way is to enable certain features or symbols with the higher bets. On a Blazing 7s machine, for example, you usually have to bet at least two coins to enable the 7s combinations. Another way is to make something more likely with higher bets. On 88 Fortunes, you're more likely to go into the bonus round when the wild symbol appears on the screen and you've bet more. On one Lord of the Rings machine, the archer bonus feature is more likely to be triggered at the higher bet levels.

One more way to increase the long-term payback for bigger bettors is to require a max-coin bet to be eligible for the progressive. Similarly, one last way is to have one or more winning combinations pay a bonus with a max-coin bet.

You said that these slots are straight multipliers with no extras for the increased bet. Based on this statement, I would say that "average percentage payout" would more accurately be called "long-term payback percentage" and that the payback is 92% regardless of the size of your bet.

So, yes, you are wasting your money betting £5 per spin because you're not getting anything extra that you don't get at 50p.


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