HP 54710A User's Reference Manual page 221

Measurements
Time-interval measurements
Vertical Quantization
The A/D converter in the HP 54720 quantizes the waveform into discrete
levels. The resolution of a time measurement cannot be any finer than the
time it takes the input signal to pass through one quantization level (one
LSB). This time will depend on the vertical resolution and the input slew
rate. The vertical resolution of the HP 54720 can vary from 8 bits to more
than 10 bits, depending on the plug-in used, the sampling rate, and the
sampling mode.
If the resolution is 8 bits, the vertical scale factor is set to 1 V/div, and the
input slew rate is 1 V/s, then the best timing resolution is 31.2 ns.
Therefore, for slowly varying edges, where sampling rate and bandwidth are
not the dominant influence on accuracy, increasing the vertical resolution at
the expense of bandwidth may improve time-interval-measurement
resolution and accuracy—a conclusion that may seem counter intuitive. You
can limit bandwidth and increase vertical resolution by turning on the digital
bandwidth limit filter located in the acquisition menu.
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