HP 54710A User's Reference Manual page 226

Measurements
Time-interval measurements
Narrow Pulse Response
If you apply a narrow pulse to the input of the HP 54720, the waveform is
affected in three ways: the height is incorrect, the 50 percent width is
incorrect, and the peak is shifted relative to the pulse as shown in
figure 13-17.
Figure 13–17
Narrow Pulse Applied to an Oscilloscope
13–41