EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 81)

Setting up and Using the Optical Sampling Oscilloscope
Optical Sampling Oscilloscope 73
Managing Measurement Parameters
Eye Mode Measurement Example
In the figure below, we have selected to show the measures of fall time,
crossing and extinction ratio, which are shown under Measurement
results at the bottom of the application. Markers associated with the
parameter that was chosen last (here the 3rd in the list - the ER) indicate
where the measurement was taken and what were the one and zero levels
from which the ER was calculated.
Note: You can also use the dual window function in the display menu to view
both the eye and pattern simultaneously.