How pokies work
A modern poker machine is a computer running a game. The spinning reels are an animation. The outcome is decided by a random number generator before the reels even start to move.
The random number generator
Inside every electronic gaming machine is a random number generator (RNG): software that produces a continuous stream of numbers, thousands of times per second, whether anyone is playing or not. When you press the button, the machine takes the current number and maps it to a position on each reel. That mapping decides which symbols land and whether you win.
Because the number is taken at the instant you press, nothing you do afterwards changes the result. Stopping the reels early, pressing harder or timing your presses does not help. It only changes when the animation ends.
Virtual reels and weighted symbols
What you see on screen is not a fair picture of the odds. A machine can use a "virtual reel" with far more stops than the physical or on-screen reel shows. High-paying symbols may occupy only one or two of those virtual stops, while blanks and low-paying symbols fill the rest.
That is how a machine can show a jackpot symbol on every reel strip yet make lining them up extremely unlikely. The symbols look evenly spread. The probabilities behind them are not.
Every spin is independent
A machine does not remember your previous spins, and it does not track how long it has gone without paying. The chance of a big win on the next spin is the same after a long dry spell as it is after a jackpot. The belief that a machine is "due" or "running hot" is one of the most common and costly misunderstandings about pokies.
Near misses
You will often see two jackpot symbols land with the third just above or below the payline. It feels like you almost won. Mathematically, a near miss is simply a loss. Researchers have found that near misses can still trigger the same excitement as a win and encourage people to keep playing, which is why they are worth recognising for what they are.
Losses disguised as wins
On multi-line machines you can bet across many lines at once. If you bet $2 across 50 lines and win 60 cents, the machine plays celebratory sounds and animations, but you have lost $1.40 on that spin. Studies of pokie players have shown that these "losses disguised as wins" are often remembered as wins. Watching your balance, not the lights and sounds, is the only reliable way to know how a session is going.
Features, free spins and bonus rounds
Bonus features are part of the same maths. Their cost is already built into the machine's overall return. A feature that pays generously when it triggers is balanced by the base game paying less. Free spins won inside a game are not free money. They are one of the ways the machine delivers its planned return.
Who tests the machines
In Australia, gaming machines in pubs, clubs and casinos are approved and regulated by each state and territory. Machines must be tested by accredited laboratories against technical standards before they can be installed, and the software is checked to make sure it behaves as approved. Regulators also set rules on things like maximum bets and a minimum theoretical return to players. The details differ from state to state.
Online pokies are a different matter. They cannot legally be offered to people in Australia, so there is no Australian regulator checking the games on offshore sites. Read more in gambling law in Australia.