Bouncing of image

There’s a emptymovieclip that loads a dynamic image whose registration point is top,left. On load, the image should bounce like a ball. I tried the bouncing ball tutorial of kirupa.com which asks to set a floor for its calculation.

The problem is, since the registration point is at 0,0 to move it up it needs some negative value say -100. It works well while going up but then after bouncing 2-3 times it settles at -100 instead of 0,0. How to make it settle at 0,0.

Any ideas on this.

thanks in advance