Anyone know how many inputs the Sidewinder Dual Strike has?

[vieo]

I'm talking about the amount of programmable buttons. I'm thinking of buying one to use in my controls though I can't seem to find a lot of information about it. From researching, I've found it has A,B,C,D,X,Y, and L&R Triggers. That's eights buttons, but from the pictures I've seen, there is another button located on the left half of the controller above the X, Y, buttons. Anyone know what that button is for? Is it used for game input or is that some sort of mode switching button?