HP 54645A User's And Service Manual page 92

Figure 4-1
Attempting to Capture Narrow Pulse
As you change the Time/Div setting (zoom in), and look at a smaller time
window around the trigger, the percentage of the acquired samples to the
displayed samples increases. For example, at 2 s/div (20 s/div across the
screen), we now display every sample acquired in that time window
(20 s / 5 ns = 4,000 samples). By zooming in to this range, we can see the
pulse of interest.
Figure 4-2
Zooming the Waveform to View Narrow Pulse
MegaZoom Concepts
Display Modes
4-9