I should explain first: There are two parking decks, both under ground. They are labeled "level 1" and "level 2". The elevator stops at both levels, and at the ground floor from where you can exit to the outside.
Anyway, who ever is responsible for this parking garage's elevator panel, did not follow the "Keep-It-Simple-Stupid"-principle (remember, this panel and its "manual" are located outside the cabin):
You want to enter the destination floor? [No, do I have to?]
Press "1" or "2".
No further operations required inside the cabin.
It's hard to notice, but the "-"-button is actually in the left bottom corner.
There are only levels 0, 1 and 2 - what are the other buttons good for? Oh I see, future extensability. Once they will excavate a whole new level 3 under ground, at least they won't have to touch the elevator panel! And what for the "-"? There is no "+"-counterpart. It all ends at level 0. This just forces you to press two buttons, instead of one. But then, it's mathematically correct, right?
So, you are standing at the ground floor, and want to go down. Unless you press "-" and then "1" or "2", the cabin will not even show up. Similar when you enter at level 2, you can then either enter "0" or "-" followed by "1". It's just ridiculous!
Now I am sure the Petronas Twin Towers must have a complex shortest-path-selection-algorithm implemented for their elevator system. I understand this decision making can be simplified if the user signals the destination of his journey already when calling the cabin. As we all know, standard elevators provide one up- and one down-button for summoning the cabin, so the cabin only stops if it's passing by in the right direction (not to mention that many people still press the wrong button or both of them once they get impatient). This ought to be enough for small to medium size systems.
Where does that thing want to go anyway? On level 0, basement parking garage customers tend to go down. On the lower levels, they most likely want to get up to the surface. OK, some weirdows might enjoy shuttling between level 1 and 2. Anyway with one and only one intermediate level, there is no real need for a complex path-optimization approach, which would depend on preceding destination input. Knowing whether we want to go up or down, followed by destination input inside the cabin should be the natural choice. Also, that's what people are used to.
I have observed elderly folks standing in front of that panel, giving up and going up or down the stairs by foot. I know this interface overstrains users. But hey, at least there are "no further operations required inside the cabin".
And I have tried, it is not a telephone, either. And in case it's supposed to be a calculator, where is the square root button? (talking about calculators, just a short off-topic-insertion at this point: you might want to have a look at Kraig Brockschmidt's online book "Mystic Microsoft" - Kraig is the creator of the original Windows 1.0 calculator and author of "Inside OLE").