I play a lot of persistence slot machines. Persistence slots, generally speaking, are those where the machine retains value from spin to spin until finally some trigger occurs which allows the player to collect that value.
Most slot machines, persistence or not, have bonus rounds of some kind. Some of these machines have multiple types of bonus rounds.
One common type of bonus round gives you a matrix of unknowns. Common shapes for these matrices are 5×5, 3×5, and 3×6. The object in this type of bonus round is that you keep touching these unknowns, one at a time, and when you do, they reveal a symbol. You keep going until you match three different symbols. It could be you’re matching Mini, Minor, Major, Mega, and Grand symbols. When you get three matching ones, you get that particular bonus.
Although these symbol names do not have to be involved, you match the Mini symbols most frequently and the Mini bonus is the least valuable. Very rarely do you match three Mega or Grand symbols. On some machines, you almost always get two Mega and/or Grand symbols along the way — but even though you have two of them, the third one is very elusive.
I’ve seen players agonize several minutes over choosing among the unknowns. If that gives them pleasure, great. After all, most of these players are playing with a big financial disadvantage and pleasure is the only payment they get for the money they spend.
Here is the way I go about it:
First, I’m only arriving at one of these bonuses while I’m playing a persistence slot machine where I calculate I have the advantage. So, the faster I go through this bonus round, the faster I collect that advantage. Agonizing over which unknown to select is a waste of time, in my opinion.
Second, I’m not sure it matters what I pick. It could be that the machine is preset to give the Grand 0.001% of the time, the Mega 0.02% of the time, et cetera et ceters, and the Mini 42% of the time. (I just made up those numbers. They are intended to be reasonable, but not matching any particular slot machine.) When the bonus round activates, the machine calculates what your bonus should be and, whatever symbols you pick, the predetermined bonus is awarded. I’m definitely not positive it works this way, but if it didn’t, it couldn’t tease you so frequently about the biggest jackpots and almost never give them to you.
Third, I pick rapidly and randomly. Sometimes I go down a row or column and pick every symbol. Sometimes I go diagonally — starting from different places in the matrix. Sometimes I don’t look at the machine very closely, put both hands up, and repeatedly tap with several different fingers as my hands go up and down.
Whichever technique I use, and whether it takes me four seconds or four minutes, eventually three symbols match and I’m paid off accordingly.
Often, when such a bonus round is finished, I’ve collected the bonus that I was “aiming for.” When that bonus goes to its reset value, the machine is no longer in a “player advantage” state. In which case, I cash out and search for an advantage elsewhere.
Almost as often, though, the bonus I hit is not the sensitive one. It could be that the Minor is high enough that I’m going to keep playing until it goes off. If the bonus round pays one of the other bonuses, the machine is still playable, and I keep going.
Sometimes, the value comes from a combination. That is, perhaps, the Minor and Major are both slightly less than the level needed to justify a play, but if I keep going until I hit either one, it’s probably a play.
At any rate, at the end of the round, I re-evaluate my position and act accordingly.

Regarding the bonus feature with picking of mini, minor, etc: I generally think that if the machine does NOT show you the unselected options after you match the required number of symbols, the outcome was predetermined. I try, when I can, to take a picture of the screen with all the symbols revealed, to see if the top prize symbols were available for me to select. That’s one of the main reasons I believe how I do; the times when I see 3 Grand symbols, I believe I actually had a chance to select them
Great point, Jon.
I have never seen all the symbols revealed after matching three (usually mini, occasionally minor). Could be they are revealed but disappear very quickly amid all the hoopla that follows matching three. I’ll pay closer attention.