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Varying a machine's hit frequency25 September 2006
Thanks for the kind words about my column.
A machine's hit frequency tells us the probability of getting a hit on any particular spin. It seems counter-intuitive, but hit frequency and long-term payback are not related — that is, we can change one without affecting the other.
Let's say a machine pays 10 coins for three double bars and 5 coins for three single bars. And, to keep the example simple, there is no payoff for mixed bars.
Assume there are 5 double bar symbols on the first reel, 4 on the second, and 2 on the third, and there are 5 single bar symbols on the first reel, 6 on the second, and 4 on the third. The following table summarizes this information:
The table shows that there are 40 ways to hit double bars and the combination pays a total of 400 coins. Similarly, there are 120 ways to hit single bars and the combination pays a total of 600 coins. Taken together, there are 160 ways to hit either single or double bars and the two combinations contribute a total of 1,000 coins to the machines long-term payback.
The next table shows what happens if we change one of the single bars on the middle reel to a double bar.
We still have 160 ways to hit single or double bars, so the hit frequency hasn't changed. But our total pays went up to 1,100, so the long-term payback has increased.
We can bring the total pays back to 1,000 by changing one of the single bar symbols on the second reel to a blank. The following table shows this situation.
The total pays is the same as in the first table, so the long-term paybacks are the same in both tables. Table 3, though, has only 140 ways to hit single or double bars, so its hit frequency is lower than the hit frequency in the first table.
The only way to change the hit frequency on a machine is to change the layout of the symbols on the virtual reels. There is no switch that the casino can throw or command that the casino can send to a machine to change its hit frequency.
Best of luck in and out of the casinos,
Send your slot and video poker questions to John Robison, Slot Expert, at email@example.com. Because of the volume of mail I receive, I regret that I can't send a reply to every question. Also be advised that it may take several months for your question to appear in my column.
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