HP 54710A User's Reference Manual page 116

You can use the markers to give you a visual indication of where you are
manually setting the top-base values on a waveform.
To use the markers to show the top-base settings
1 Press the Markers key.
2 Select the Measurement mode.
3 Press the blue shift key, V amptdV amptd, then select channel you are using.
4 Press the Define meas key.
5 Set Top-base to User defined.
As you adjust the values of Top and Base, the markers give you a visual
indication of where you are positioning them on the waveform.
If the marker values are much greater than the top-base values, the markers
may be clipped off the screen.
Define Measure Menu
Top-Base
7–7