dr_panther,

thanks for your reply.
Unfortunately the result is not what I' m searching for.
In the picture below the blue line is the result of the code you provided while the red line ( hand painted) is the regression straight line I need.
Furthermore I would avoid to pass past data to the method calculation of the linear regression . For the linear regression you need only the present data for the calculation of the straight line.

https://drive.google.com/open?id=0B7OAmRgfpHP-WkRjSk1uV3BVT2s

Thanks in advance, Andrea