HP 54620A User's And Service Manual page 145

Ensuring Accurate Measurements
Glitch Detection
If several transitions occur between samples, the analyzer displays only one
glitch. Also, when multiple samples are mapped to a single display
pixel—which is often the case—a display in category 2 or 4 will be the likely
result, if any glitches occurred between those samples.
Figure 46
Glitch Display
Aliasing and Glitch Capture
In a sampled device, aliasing occurs when the same set of sampled data could
be used to reconstruct many different waveforms, because of insufficient
data. See figure 47, where, because of insufficient sampling rate, the
reconstructed waveform would be only one-third the frequency of the
original.
Figure 47
Aliasing
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