When manual trigger level selection has been turned on using the “At/Norm.” button, the trigger level can be set using the “Level” wheel. Use the “+/-“ button to set whether the ascending or the descending flank shall trigger the sweep.
The following images show examples for different trigger settings:
The “At/Norm.” button is on (=manual trigger level setting),
the “Level” wheel is turned to a position lower than the lowest voltage of the signal,
therefor the signal cannot be triggered, the screen remains empty.