When you press "View diagram" in S.M.A.R.T. Details view the S.M.A.R.T. diagram is shown.
On the S.M.A.R.T. diagram you can see the graphical representation of the Hard Drive Inspector T.E.C. prediction algorithm. The diagram shows three lines:
The point where the threshold line intersects the trend line is the predicted point when S.M.A.R.T. attribute value achieves its T.E.C.
Double click on the diagram surface to see the attribute's value history.