HP 54710A User's Reference Manual page 104

Example The mainframe's CAL signal is a voltage source. You cannot use it to
Other devices calibrate to the probe tip when units are set to Ampere, Watt, or unknown.
Instead, you set the external gain and external offset to compensate for the
actual characteristics of your probe or device. If you do not know its actual
characteristics, you can refer to the specifications that came with the probe
or device. The following steps show you how to do this.
Set Atten units to ratio.
1
Set Probe atten to 1:1.
2
Set Units to Ampere, Watt, or unknown.
3
Set Ext gain to the actual gain characteristics of your probe or device.
4
Set Ext offset to the offset that is introduced by your probe or device.
5
Calibrate probe
Connect a voltage probe from the plug-in to the CAL signal on the mainframe,
then press the Calibrate probe softkey. The oscilloscope calibrates to the tip
of the probe by setting the probe attenuation to the actual attenuation ratio
of the probe. The oscilloscope also automatically compensates for any offset
that the probe may introduce.
Channel Menu
Probe
6–9