HP ESA-L1500A User's And Calibration Manual page 85

Front-Panel Key Reference
Frequency
moves the signal that is nearest to the active marker to the center of
Signal Track On
Off
the display and keeps the signal there. Sig-Trk appears in the
upper-right corner of the display. An (*) may appear in the upper-right
corner of the display while the spectrum analyzer is verifying that it
has the correct signal.
Pressing
turns off the signal track function.
When signal track is on and the span is reduced, an automatic zoom is
performed: the span is reduced in steps so that the signal remains at
the center of the display. If the span is zero, signal track cannot be
activated. Key Access:
84
,
Signal Track On Off Preset
Frequency
, , or
Marker Normal Marker All Off
Chapter 4