HP 4934A Operating And Calibration Manual page 27

RECEIVER
11 Display the received level and frequency using the DISPLAY key (RCV indicator
will be lit).
Receiver Reference
12
If attenuation relative to a reference is required, press
LEVEL ZERO
when the
reference signal is present and stable (for attenuation distortion measurements
this is normally at 1004 Hz). This changes the level reading from an absolute
value in dBm (in the left window) to a relative attenuation value in dB. All
subsequent received level readings will be relative to this value. A negative
reading indicates a level higher than the reference level.
Pressing
LEVEL ZERO
a second time changes the level reading back to
absolute units in dBm.
To change the transmitted frequency, return to step 2.
N OT E
Error Codes will be displayed if the input level to the receiver is too high or unstable
(see the error codes in Chapter 1).
Making Measurements 2-9