338 Keysight M8000 Series of BER Test Solutions User Guide
6 Setting up Analyzer
4 Click the sample delay marker, and keep the left mouse button held
down, while dragging the marker to a position that is supposed to be
between the transitions of the signal. Alternatively change the sample
delay setting in the parameter editor.
This does not have to be perfect, the goal is just not to sample at the
signal transitions.