HP 54710A User's Reference Manual page 32

How the Oscilloscope Works
Sampling Overview
Equivalent-time sampling
The equivalent-time sampling mode is typically used on repetitive signals,
which allows the oscilloscope to acquire data continuously. The sample rate
is 500 MSa/s, but the data from many acquisitions are interleaved, which
results in a much higher effective sample rate.
You can still use the equivalent-time sampling mode for single-shot
applications. Because the interpolation filter is not available in the
equivalent-time mode, the maximum single-shot frequency you can
reasonably view and also avoid aliasing is about one-tenth the sample rate, or
50 MHz.
The HP 54711A and HP 54712A plug-ins are best suited for equivalent-time
sampling because they allow access to the highest system bandwidths.
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