All 4 Slots

Nowadays, the resulting symbol combinations are dictated by a computer chip inside the slots itself, rather than by the activity of the spinning reels.
Predetermined stopping points controlled by the computer chip are used to stop each reel,which in turn, are regulated by small digitized bursts of electricity.

Although this sounds like pre-programming, which it is, the pre-programming that involves the payout percentage of a machine is determined by another device – the random number generator (RNG).
With RNG in place, each spin of the reels has an equal chance of striking a big win.

With RNG engaged hundreds of numbers ranging from one to several billion are being generated each second.
When you press the play button, the computer records the next 3 numbers from RNG. The first number is used to determine the position of the first reel, the second for the second reel and the third number for the third reel.

The calculation that is used invloves dividing the RNG generated number by multiplies values of 32, and up to a value of 512.

After running this calculation, we get 14 with a remainder of 2. The remainder is very important as it shows there are only 32 possible end results and the computer then maps the 32 possible values out as stops on a computerized reel of 32 stops.

The computer system is responsible for governing whether a machine is going to be loose or tight, and just how much money it pays out over the long run. Not only is less oversight required, the out come will always be mathematically presice.

So you have to be very clever mathematically to watch and learn the reels, and some people spends months learning a slot machine, and when to play.