Interview with Gaming Mathematician/Game Designer Diana Gruber

In the first part of a series here at VegasSlotsOnline, we explore the secret life of the boys and girls who put together the slots you play and love (and of course, win huge sums of money at on a daily basis).

First up, legendary game mathematician Diana Gruber, who started out on a rusty IBM coming up with frameworks for slot machines before going on to help develop some of the most popular slots around for manufacturers like Bally and Playtech.

How Did You Became a Game Developer?

In the early days of our marriage, Ted and I did not agree on an expensive purchase. He wanted to buy an IBM PC in 1987 and I thought it way too expensive. He won me over by promising to put the machine to work and make it pay for itself, and I agreed we should try to write some games.

The only problem was, there wasn’t any way to draw graphics quickly on a first generation PC. We had to figure out that part from scratch. So we started game development at a very low level. I would tell Ted what I needed (point, line, rectangle), and he would give me graphics functions. He did it by reverse engineering the video hardware and writing code in assembly language. It was a brilliant accomplishment, and Fastgraph was born. As I wrote shareware games, Ted kept building Fastgraph, and eventually we sold that too. Our plan worked, and our little computer supported us and things grew from there.

My first game was video poker, and my second game was a slot machine called “Microbucks”. It was a play on the name “Megabucks”.  Do you get it? Personal computers were called microcomputers back then. It was the style at the time.

Fastgraph sold like hotcakes and supported us all through the 90’s. It had a good run, until Microsoft put the brakes on the whole thing. They released a competing product called “DirectX”, and gave it away for free. That was the end of our ability to compete. So Fastgraph faded and Ted and I moved on to other things. Ted went to work on a government project, and I started working at Bally.

“Micro Bucks was designed for the DOS system in 1993.” (FoxHack)

I enjoyed my time at Bally very much. I worked with some wonderful people and we designed some really great games. A couple of my favorites recently showed up as product placements in movies. I have a picture of Kristin Wiig standing next to a bank of Blazing 7s Hot Shots in the movie “Girl Most Likely” (see image above). I also have a picture of Robert De Niro sitting next to a bank of MultiPlay Blackjack in the movie “Last Vegas“. Releasing a game is a thrill, but seeing your game in a movie is a meta-thrill.

What Do You Mean by “Designing” a Slot Machine?

It takes many people to design a slot machine. My role is mathematician. I produce a formal document that describes exactly how the slot machine works. I calculate the odds of everything that can possibly happen and then assign awards to events based on their likelihood. It all goes into a document called a par sheet. The par sheet is the first and most essential thing you need to build a slot machine. You can’t really build one without it.

My par sheets include detailed information about the pay table, the reels, the symbols, the mini games, wild symbols, progressive jackpots, and so on. If the engineers or the gaming bosses want to know how often the free spins are triggered, they will find the information in the par sheet.

How Many Slot Machines Have You Designed?

I couldn’t say for sure, but I crank them out pretty fast. I do about 30 games per year, and I’ve been at this for 15 years, so that’s a lot of games.

Have You Noticed Any Changes in the Industry While You Have Been Doing This?

Yes, absolutely. In the early days of Microbucks, the slot machines all looked very similar. They all used the same symbols, even the video slots. You would see fruit, bells and bars everywhere. By the time I started working at Bally, things were getting more interesting. Aristocrat and IGT released some “Aussie-style” games.  By that I mean games like Queen of the Nile and Cleopatra. The style involved free spins, a pick bonus and royal flush symbols: Ace, King, Queen, etc. The style caught on to the point it has become ubiquitous. You see Aussie-style games everywhere.

At the same time, another classic style was on the rise and I can take some credit for that one. An “Option Buy” game is a game where you get a better return for playing more coins per line. I designed many variations of Blazing 7s and Bonus 7s, and those games are everywhere.

Another trend over the past decade was the rise of Class II games in tribal casinos. This curious hybrid of bingo-driven reel spinners is mathematically challenging and has provided me with a few nice paychecks.

Wild symbols became more interesting with the invention of the exploding wild. The earliest example I can think of is Atari Pong from Bally. Besides the exploding wilds, that game also had the first bonus skill game in Nevada. Exploding wild games are exciting, and over time they have become more complex. Vertical expansions, stacked wilds, horizontal expansions, block expansions, the list goes on. Wild symbols do many surprising things these days.

Diana was responsible for developing the math on versions of Bally’s classic Blazing 7s Progressive slot.” (Bally)

Another interesting trend that seems to have faded is community bonuses. An example would be 6 slot machines in a bank linked to a single large screen. During the bonus, all the players in the bank get to pick a suitcase or catch a fish. Community bonus math and engineering are highly technical, meaning it is a huge investment in development time and resources. I can’t say how often that investment has paid off, but I am not getting requests for that kind of math any more.

When You Design a Slot Machine, Do You Know if It Is Going to be a Hit?

No, nobody knows that. But often, I can spot which ones are going to fail. There are things that will almost certainly guarantee failure, and the biggest one is a skewed distribution. If your distribution has too many large awards, then your players will suffer. They will not get enough low-end hits, and they will lose their bankroll right away and give up. I can predict how likely that is to happen. I simulate everything, and I can tell you if your distribution is out of whack. But I can’t tell you if your game will be a hit. That depends on factors that have nothing to do with me.

Diana designed the math for Playtech’s popular branded slot, Rocky.” (Playtech)

Is Social Gaming the Same as Gambling?

No, it is not. Social gaming is the same as shareware. I have an intimate acquaintance with both industries, and I am convinced social gaming resembles shareware more than it resembles anything else.

The goals are different. In gambling, you place a wager and expect a return. In shareware, you pay a licensing fee to use a software product. It isn’t the same thing at all.

Is That an Important Distinction?

Yes, because gambling is regulated and shareware is not.  In a shareware game, anything goes. You can completely control the player experience. You can make their luck run in streaks. You can give them volatility like a roller coaster. You can change the RTP so they win all month and go broke on payday. If you have an idea and you think it will give you a competitive edge, there is nothing stopping you from trying it in a social gaming environment.

What Does the Future Hold?

The future couldn’t be brighter for small and medium sized slot machine development houses. Slot machines are popular and addicting. The market is expanding and the audience is growing. In the past, mathematics was an obstacle to breaking into the slot development industry, but that is no longer true. If you want to launch a slot machine company, math is available for you. With world-class math, your company can grow to rival the glory days of Bally, IGT and Aristocrat. Let me help you with that.

Thanks for your time Diana – Best of luck in the future and come back to chat us again soon!

You’re welcome! Thanks for having me, take care.

You can read more about Diana Gruber at her website,