The process is divided into two steps: First, using the script 1d_ascii_generate_normalization_points.py (download here) the spectrum is plotted in an active graphics window and the grid points for the continuum fit can be defined with the mouse pointer. Their wavelengths are displayed in the graphic. The little windows displaying the wavelengths can be moved for better readability (active graphic). The graph is then saved manually in the graph window using the save function.
In the next step the wavelength of the continuum points will be needed.