HP 16534A User Reference page 19

Autoscale
Autoscale Algorithm
Displaying the Waveform When the autoscale algorithm is complete,
the oscilloscope automatically starts running, and displays waveforms
for the inputs that have been selected. The run mode (single or
repetitive) that was selected prior to running autoscale is the run mode
executed when autoscale is completed. If a run mode has not been
selected prior to running autoscale, the single mode run is executed.
The channel and time base fields are updated (if necessary) to reflect any
changes made by the autoscale algorithm. The trigger settings are also
changed by the autoscale algorithm and an edge mode trigger with channel 1
or channel 2 is selected. The trigger source is set to channel 1 or channel 2.
Even if the scaling is based on a higher-numbered channel, it will not be
used as the trigger source. Instead, the trigger source will default to channel
1.
The trigger point on the waveform is determined by the trigger level set by
the autoscale algorithm. The trigger point is displayed as a dotted vertical
red line at the center of the screen when Delay is set to 0 s.
What the Autoscale Algorithm Does When a Signal Cannot be Found
When a signal cannot be found on any of the vertical inputs, the oscilloscope
displays the advisory messages "No signal found" and "Original setup
restored." The autoscale algorithm toggles the Auto-Trig field to On, which
places the oscilloscope in the automatic trigger mode. The oscilloscope
then displays the message "Auto triggered." The automatic trigger mode
allows the oscilloscope to sweep automatically and to display a baseline
anytime a trigger signal is not present.
2-5