Keysight Technologies U1253B - Figure 4-5 Decibel Measurement Setup; Setting Db Measurement

4 Changing the Default Settings
118 Keysight U1253B User’s and Service Guide
Setting dB measurement
The decibel unit can be disabled by setting this to “OFF”. The available options are
dBm, dBV, and OFF. For dBm measurement, the reference impedance can be set
by the “dBm-R” menu item.
Figure 4-5 Decibel measurement setup