Ask the Slot Expert: The advantage of overlay symbols

Last week I gave you a homework assignment using a slot I've been playing a lot recently, Diamond Quick Hit Link. Let's start with a description of the machine.

Diamond Quick Hit Link, like many other slots today, has three bonus features with BS meters that don't show you how close you are to triggering the bonus. On this machine, the BS meters are big green, red, and purple dollar signs with firecrackers on them. When the corresponding symbols appear on the screen, rockets shoot up from the symbol to the appropriate dollar sign. The rockets may light some of the firecrackers.

It doesn't matter how many firecrackers the rockets light. The meters are meaningless. You're no more likely to trigger the bonus when almost all of the firecrackers are lit compared with when none or few of them are lit.

The three features are:

• Green - Extra Spins: Green firecrackers that award an extra spin may appear on the last reel during the bonus spins.
• Red - Reels Up: The reels expand from 3 x 5 to 6 x 5 for the bonus spins.
• Purple - Rocket Quick Hits: Rocket symbols may shoot onto the screen and explode into a Quick Hit symbol during this bonus. The symbol itself may have one, two, or three rockets that will be fired onto the screen on the next spin. Those symbols may also have rockets.

One aspect of this game that I really like is that the symbols that trigger these features are not symbols on the reels. They are symbols that appear on top of a reel symbol and then disappear once their rockets are launched. Getting one of these symbols cannot ruin a winning combination.

The green firecrackers that award extra spins operate the same way. When they appear on the screen, they explode, increase the free games remaining counter, and then disappear to reveal the symbol on the reel.

Now your homework assignment.

You are a slot designer. You want to reward players who bet more.

What advantage do these "overlay" symbols have over reel symbols?

Let's step into the Wayback Machine and look at how designers increased the payback on a machine without any bonus features like an old, traditional, reel-spinning Double Diamond machine.

I compared two Double Diamond PAR sheets, one for quarters and the other for dollars. The dollar machine paid back a little more than the quarter machine. The designers increased the payback by decreasing the number of ways to make single bars and increasing the number of ways to make double or triple bars. They did this, in concept, by taking some of the virtual stops that mapped to single bars and making them double or triple bars instead. To be more accurate, they decreased the number of virtual stops mapped to single bars and increased the number of virtual stops mapped to double or triple bars. A specific virtual stop was not changed from single bars to double or triple bars.

Back in this era, the only way designers could reward higher denomination players with higher paybacks was to change the virtual reel layout.

Now let's come back to the present day and look at a machine with one or more bonus features. The designers can leave the reels on the base game the same at all bet levels and make the bonuses pay more for players betting more.

Finally, let's make the triggering symbols overlay symbols instead of reel symbols. The designers can leave the base game the same and have the algorithm that determines whether to display an overlay symbol on the spin make the symbol appear more frequently for a higher bet player or make the symbol trigger the bonus feature more frequently.

Of course, designers can also make the base game pay back more.

The advantage overlay symbols have over reel symbols is that designers don't have to change the reel layout to change the payback.

Designers have three tools in their arsenal to reward players who bet more: make the base game pay back more, make the bonus feature pay more, and make a bonus-triggering overly symbol appear more frequently.

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