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Ask the Slot Expert: Four ways to determine the result of a spin on a slot machine

8 September 2021

This week let's take a look at four ways the results of a spin on a slot machine can be determined.

The first and oldest (and probably most prevalent) method is the Random Number Generator (RNG), the digital implementation of the method used in the mechanical and electro-mechanical slots that ruled the slot floor until the computer-controlled slots took over. The old machines contained a mechanism that attempted to stop the reels at a random place on each spin. The machines also had mechanisms to read where each reel stopped and then pay out anything won.

Computer control of the slot machine came in the 1980s. These machines got rid of the "random stop" mechanism and replaced it with the RNG. The machines used a number generated by the RNG to determine where to stop a reel. The machines still have a mechanism to read where the reels have stopped, but now it's not used to determine the result of the spin. The computer already knows where the reels were supposed to stop. It's used to ensure that the reels stopped where the computer told them to stop and, if not, the machine will raise a Reel Tilt error.

The RNG is so simple. But it's also considered to be gambling in some places. So when these places wanted to have gambling without having gambling, they had to look for another way to determine where to stop the reels on a slot machine.

If a state allowed charitable bingo games, then Native American tribes could run bingo games too. Many opened bingo halls. The real money is in spinning reels, though, so they looked for a way to turn a bingo drawing into a slot machine.

Enter the Class II slot machines. The Indian Gaming Regulatory Act defined three classes of gaming. Class I is social gaming for minimal prizes. Class II is bingo and pull tabs. Class III is gambling -- table games and RNG-based slot machines and pretty much anything else that doesn't fit in Class I or Class II.

To find the results of a spin, a Class II slot machine joins a bingo drawing that is conducted on a central server. The central server draws the bingo numbers and sends them down to all of the machines participating in the drawing. A machine determines its results by the pattern filled on its electronic bingo card. These patterns aren't necessarily the fun ones, like the Champagne Glass and the Dollar Sign, just a pattern on the card.

The central server won't conduct a drawing until a minimum number of players have joined it. Players who like to play in the wee hours have told me that they sometimes have to wait to see the results of a spin until enough players have joined a drawing. By contrast, the RNG is not only always ready to supply a result, it's constantly generating new results even when its machine is not being played.

Now let's say you're a state that wants slot machines but not gambling. Your lottery sells scratch-off tickets. Is there any way to turn a scratcher into a slot machine?

This method is known as Finite Outcome. A central server maintains a pool of possible outcomes, like the boxes of scratch-off tickets the lottery commission prints for a particular scratch-off game. When a player hits the Spin button on a machine, the machine requests an outcome from the central server. The central server chooses an outcome from the pool appropriate for the game on that machine. The machine then spins the reels and stops them on the outcome received from the central server.

What happens when a pool is used up on the central server? No problem. Just like Lay's potato chips, it will make more. When a pool is depleted, the central server just creates a new pool.

I thought I had seen it all in how jurisdictions allow slot machines without allowing gambling, but I learned of a new one last week. Say you're in a state that allows betting on horse races. Is there any way to turn the results of horse races into results on a slot machine?

I wrote about this method, Historical Horse Racing, last week. Let's take a more detailed look this week. This description is based on the method described in the patent cited below.

To determine the results of a spin, the method uses three races with 10 horses each. Each finishing place in each race is assigned to a bit in a binary number. For example, Race 1 Place 1 may be assigned to bit 1 and Race 2 Place 5 may be assigned to bit 20. The alignment is arbitrary.

For each race, there is a predicted order in which the horses will finish. And, of course, there is the actual order in which the horses finished.

The method checks to see which predictions are correct. If the prediction for Race 1 Place 1 was horse 6 and horse 6 did finish first in Race 1, the method assigns a 1 to bit 1. If the prediction for Race 2 Place 5 was horse 3 and horse 9 actually came in fifth, the method assigns a 0 to bit 20.

To recap, there are 3 races with 10 horses each, so there are a total of 30 predictions. Each prediction corresponds to a bit in a binary number, so the binary number has 30 bits. When a prediction is correct, its corresponding bit is set to 1. Otherwise the bit is 0.

After all of the predictions have been evaluated, we have a 30-bit binary number. (A sample 30-bit binary number is 100010000000100010101111000000.) There is a table of results that tells us the result assigned to each number. The method looks up the result that corresponds to the number calculated from evaluating the predictions.

There is another step that complicates the process. Can you imagine players entering in 30 predictions for each spin? Most people just want to hit the Spin button. The system will calculate the initial predictions for each race. The patent allows for the player to alter the predictions, but I can't imagine any player doing that.

I'm still shaking my head over this method.

Source: Patent: System and Method of Wagering on a Plurality of Events


Here are the latest figures from https://www.cdc.gov/covid-data-tracker/#cases_totalcases.

Totals Weekly Increases
US NV US NV
Date Cases  Deaths  Cases  Deaths  Cases  Deaths  Cases  Deaths 
 09/07   40,085,811   647,461   394,595   6,583   975,725   10,076   5,237   104 
 08/31   39,110,086   637,385   389,358   6,479   1,113,414   9,385   7,592   173 
 08/24   37,996,672   628,000   381,649   6,306   1,045,491   7,507   8,117   116 
 08/17   36,951,181   620,493   373,649   6,190   959,978   4,715   7,065   150 
 08/10   35,991,203   615,778   366,584   6,040   819,524   3,987   7,652   122 
 08/03   35,171,679   611,791   358,932   5,918   622,832   2,279   7,489   81 
 07/27   34,548,847   609,012   351,443   5,837   652,251   2,394   8,347   79 
 07/20   33,896,296   606,618   341,096   5,758   169,933   1,478   3,351   28 
 07/13   33,726,363   605,140   339,745   5,730   181,047   1,959   4,982   33 
 07/06   33,545,316   603,181   334,763   5,697   75,104   1,373   2,234   27 
 06/29   33,470,212   601,808   332,529   5,670   87,507   2,057   3,020   24 
 06/22   33,382,705   599,751   329,509   5,646   75,420   2,157   1,930   22 
 06/15   33,303,285   597,594   327,579   5,624   95,797   2,293   1,560   17 
 06/08   33,207,488   595,301   326,019   5,607   114,250   3,762   2,271   21 
 06/01   33,039,238   591,539   323,748   5,586   123,333   3,709   991   27 
 05/25   32,969,905   587,830   322,757   5,559   174,125   4,234   1,676   26 
 05/18   32,795,780   583,596   321,081   5,533   223,966   4,230   2,301   27 
 05/11   32,571,814   579,366   318,780   5,506   303,856   4,687   2,541   33 
 05/04   32,267,958   574,679   316,239   5,473   343,348   4,908   2,559   40 
 04/27   31,924,610   569,771   313,680   5,433   383,163   4,958   2,747   65 
 04/20   31,541,447   564,813   310,933   5,368   464,556   5,072   2,590   36 
 04/13   31,076,891   559,741   308,343   5,332   480,061   5,321   2,986   57 
 04/06   30,596,830   554,420   305,357   5,275   448,935   7,124   3,084   38 
 03/30   30,147,895   547,296   302,273   5,237   439,510   6,793   939   63 
 03/23   29,708,385   540,503   301,334   5,174   388,928   7,446   1,863   53 
 03/16   29,319,457   533,057   299,471   5,121   381,695   8,362   3,078   81 
 03/09   28,937,762   524,695   296,393   5,040   480,902   11,573   2,413   83 
 03/02   28,456,860   513,122   293,980   4,957   463,356   14,129   2,835   75 
 02/23   27,993,504   498,993   291,145   4,882   451,083   13,923   2,406   162 
 02/16   27,542,421   485,070   288,739   4,720   602,906   21,411   4,149   198 
 02/09   26,939,515   463,659   284,590   4,522   779,305   21,828   5,444   244 
 02/02   26,160,210   441,831   279,146   4,278   1,007,777   22,004   7,249   249 
 01/26   25,152,433   419,827   271,897   4,029   1,312,565   23,385   10,324   250 
 01/19   23,839,868   396,442   261,573   3,779   1,317,119   21,318   11,324   279 
 01/12   22,522,749   375,124   250,249   3,500   1,790,345   22,660   17,217   294 
 01/05    20,732,404   352,464   233,032   3,206   1,499,561   18,435   14,655   233 
 12/29   19,232,843   334,029   218,377   2,973   1,258,540   15,460   12,493   186 
 12/22   17,974,303   318,569   205,884   2,787   1,656,411   18,537   16,472   239 
 12/15   16,317,892   300,032   189,412   2,548   1,494,763   17,247   18,825   229 
 12/08   14,823,129   282,785   170,587   2,319   1,375,502   15,483   18,418   175 
 12/01   13,447,627   267,302   152,169   2,144   1,114,175   10,286   15,942   121 
 11/24   12,333,452   257,016   136,227   2,023   1,197,199   10,784   14,130   106 
 11/17   11,136,253   246,232   122,097   1,917   1,099,790   8,501   11,115   65 
 11/10   10,036,463   237,731   110,982   1,852   767,645   6,838   8,868   68 
 11/03   9,268,818   230,893   102,114   1,784   588,207   5,809   5,936   35 
 10/27   8,680,611   225,084   96,178   1,749   492,026   5,585   5,238   (10) 
 10/20   8,188,585   219,499   90,940   1,759   401,037   5,053   4,501   48 
 10/13   7,787,548   214,446   86,439   1,711   351,270   4,886   3,910   48 
 10/06   7,436,278   209,560   82,529   1,663   306,965   4,962   3,232   36 
 09/29   7,129,313   204,598   79,297   1,627   303,616   5,136   3,058   54 
 09/22   6,825,697   199,462   76,239   1,573   288,070   5,370   2,196   82 
 09/15   6,537,627   194,092   72,043   1,491   250,265   5,404   1,825   65 
 09/08   6,287,362   188,688   72,218   1,426   282,919   5,638   2,734   92 
 09/01   6,004,443   183,050   69,484   1,334   251,790   5,291   3,237   104 
 08/25   5,752,653   177,759   66,247   1,230   330,411   7,889   4,076   125 
 08/18   5,422,242   169,870   62,171   1,105   358,071   7,463   4,973   114 
 08/11   5,064,171   162,407   57,198   991   365,353   7,203   5,776   117 
 08/04   4,698,818   155,204   51,422   874   418,683   7,532   7,367   109 
 07/28   4,280,135   147,672   44,055   764   460,996   7,042   7,130   91 
 07/21   3,819,139  140,630  36,195  674  463,682  5,395  8,181  57 
 07/14   3,355,457   135,235   28,744   617   422,861   5,102   5,607   57 
 07/07   2,932,596   130,133   23,137   560   351,367   3,394   5,006   24 
 06/30   2,581,229   126,739   18,131   536   278,941   6,406   4,367   26 
 06/23   2,302,288   120,333   13,764   510 
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