HP 8920A Application Handbook page 217

On the Test Set using the knob and data entry keys:
22. From Controls, select Main.
23. Select Marker from the Choices field.
24. Use the Marker position to measure the response.
Notch depth is displayed as Lvl.
Bandwidth (3 dB points) is measured using the LVL and Freq display.
The notch or band-pass frequency can be changed by trimming the coaxial
filter in small increments.
Using the Tracking Generator
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