To extend a linear form by placing data points

Select (Modify Form).
Click Extend a Linear Form icon.
From the Method option menu, select Add Distance.
Select a linear form to extend. The form will be extended on the end closest to where the form is selected.
Enter a data point to define the new length of the linear form. The data point is projected perpendicular to the baseline of the linear form. The projected point is the new start or end point of the linear form.