HP 54645A User's And Service Manual page 14

Getting Started
The HP 54645A/D high-speed display can be used to isolate
infrequently changing signals. You can then use the characteristics of
these signals to help refine the trigger specification. See figure 1-2
below. For more information on triggering, data acquisition, data
examination and measurement, and configuration, see chapters
3 and 4.
Figure 1-1 Figure 1-2
Using the HP 54645A/D Oscilloscopes, and Refining the Trigger Specification
1-3