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Ask the Slot Expert: What Can Casinos Change on a Slot Machine?

1 October 2014

By John Robison, Slot Expert™

Can you tell me what a casino can do to a newly acquired slot machine?

Does the slot machine come with a preset payout percentage? Can the casino change the payout percentage?

I assume the slot machine has a preset time period for the payout percentage. Can a casino change the preset time for the payout?

Can a casino change some of the minor bonus features for the better or worse?

What can the casino do to a new slot machine? Put it on the slot floor.

When the casino orders a slot machine, it specifies the long-term payback percentage it wants installed on the machine from the percentages available for the game. Depending on the jurisdiction, the casino may or may not be able to change the payback percentage later on. In Nevada, the casino can change the percentage by ordering the new percentage chip from the manufacturer, swapping chips in the machine, and filing the appropriate paperwork with the state to inform it of the change.

Some machines support downloadable software. On these machines, the software can be sent from a central server and the machine does not have to be opened. There are strict rules about when the software change can take place, so the casino can't change a machine while someone is playing it.

There is no preset time period for the payback percentage. A machine's actual payback percentage will get closer and closer to its long-term payback percentage as the machine gets more play. Even after tens of millions of plays, the actual payback percentage might be a few tenths of a percentage point off from the long-term percentage.

Many things on a slot machine cannot be changed from a configuration menu. Making some aspects configurable can open the machine up to cheating. Volume is safe to be configured -- some machines even let you adjust the volume yourself -- but how about denomination? A slot technician was caught cheating the casino by changing the denomination on a machine for his friend. He would change a dollar machine to a dime machine. Then his friend would insert $50 and get 500 credits. Then he would change the machine's denomination back to dollars and his friend would cash out with a $450 profit.

I have a question that I don’t recall ever being addressed.

Once the fair decision has been determined via the RNG, can the program manipulate what is seen by the player so that it looks like a “near miss"? For example, if the fair result is three symbols in a row, can the program show the fourth symbol just one position off even though the RNG didn’t put that symbol there, as long as it doesn’t change the result of the game? (This may be a little difficult given multi-line games, but still, very do-able).

This would have the effect of making players think that the machine is “getting close” to hitting. Of course, those that read your column know that this thinking is nonsense.

Most, if not all, juriscictions have slot regulations that require that the machine show the result determined by the RNG with absolutely no alterations. But this was not always the case.

In the 80s, one of the early computer-controlled slots was made by Universal. The software in these machines chose either a specific winning combination or loser. If loser was the result of the spin, the machine selected a losing combination from a table of losing combinations that contained a high percentage of near misses. The psychology behind this method is that a losing combination of jackpot-jackpot-blank is more exciting than bar-bar-blank and, as you pointed out, might lead some people to think that the machine is close to paying. Because high-paying symbols landed on the payline more frequently when they were part of a losing combination than when they were part of a winning combination, this "secondary decision" of choosing a losing combination was deemed deceptive. It made it seem like hitting the jackpot was more likely than it really was.

As a result, Nevada changed its slot regulations to require that the output from the RNG be used to choose which symbols land on the payline and that the result cannot be altered in any way. New Jersey, the only other gaming jurisdiction at the time, followed suit and all Universal machines had to be re-programmed to follow the new regulations.

Today's reel-spinning slot machines still have near misses, but they're all a result of how the virtual reel are laid out. Near-the-payline near misses occur because the blanks above and below the jackpot symbol appear more times on the virtual reel than the jackpot symbol. On-the-payline near misses occur because the jackpot symbol appears more times on the first two virtual reels than on the third. In both cases, the symbols land on the payline with a frequency directly related to how many times they appear on the virtual reel.

Near misses may be great "fish that got away" stories, but thinking that a near miss means a machine is close is, as you rightly point out, nonsense.

Send your slot and video poker questions to John Robison, Slot Expert™, at Because of the volume of mail I receive, I regret that I can't reply to every question.

Copyright © John Robison. Slot Expert and Ask the Slot Expert are trademarks of John Robison.


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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