In 1984 Inge Telnaes received a patent for a device titled, "Electronic Gaming Device Utilizing a Random Number Generator for Selecting the Reel Stop Positions." International Gaming Technology IGT bought the Telnaes patent and now all slot manufacturers using what has come to be known as Talneas mapping or reel mapping must license the patent from IGT. This device allowed for the creation of what we call the virtual reel.
While a physical reel may have 22 symbols of stops on it a virtual reel can have 32 up to 256 or even virtual stops. The virtual stops are assigned to one of the symbols on the physical reel. Here are the possible outcomes for different numbers of virtual stops.
Stops Outcomes
32 32,768
63 262,144
256 16,777,216
512 134,217,218
Since you don’t know the number of virtual stops a machine has it is impossible to determine what the odds are for hitting the jackpot. The number of each symbol on the reel can also affect the return.
Look at this example for a machine that has 32 stops on each reel. The total combinations are 32,768. Listed below is the payouts and number of occurances out of 32,768
Pay table is:
Symbol Pays Occurrences $Payout
3 Sevens 250 30 7,500
3 Bars 75 80 6,000
3 Cherries 12 12 144
Any 2 cherries 8 476 3,808
Any Cherry 2 6180 12,360
Total wins $29,812
Total bets $32,768
Return 90.979%
Here are the symbols on each reel.
Symbols Reel 1 Reel 2 Reel 3
3 Sevens 5 2 3
3 Bars 5 4 4
Cherries 2 3 2
Blanks 20 20 23
Now if you were to change the number of bars on reel 3 from 4 to 5 the return would increase to 95.577%.
If you decrease the number to 2 the payback would be reduced to 81.824%
If you changed the cherries on the first reel from 2 to 3 the payback would increase to 99.072
This example shows you how adjusting the symbols can affect the return of the machine.