About the iphone acceleration axis

I need to check carefully about this.

According to my understanding and the scheme axis definition of the iphone, when I move the iphone, for example, up towards, the acceleration in the Y axis should be positive and if the iphone is moving down the acceleration should be negative. (both movements starting from zero movement).
Just like the graph in the left side.
Surprisingly, in fact, the behavior is completely opposite!!
I mean, the acceleration is negative when the iphone is moving in the up and positive when is moving down!
What the heck!
What do you think?
Is that correct?… I should check again my basis in physics!

No, wait!
Yes, Now I realize its logical!
In fact, the force of acceleration is acting against the direction of the movement. The sensors actually are measuring the rate if increase of velocity. I see.
The only thing I have to do is to change the sign. If the acceleration is positive, then the movement in fact is negative.