Agilent Technologies PSA Series Manual page 33

Measurement Concepts
Calibration/Normalization
position/level settings are applied to the displayed trace data.
Normalized reference position is indicated by arrowheads at the edges
of the graticule.
Reconnect the DUT to the analyzer. Note that the units of the reference
level have changed to dB, indicating that this is now a relative
measurement.
Chapter 2 33