EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 120)

Measurement Definitions
112 PSO-100
Timing Jitter
Timing Jitter
The timing jitter of an NRZ eye diagram is a measurement of the variance
in time locations of the crossing point. Horizontal time histograms are
constructed, and the histogram having the smallest variance determines
the crossing point. The standard deviation of this histogram determines the
RMS timing jitter and the extreme points (the largest and the smallest time
value) in the histogram determine the peak-to-peak timing jitter.
Histogram window
Histogram
Peak to peak