B&K Precision 2542B-GEN - Manual - Manual (Page 67)

Basic Operation
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After the line disappears, the trigger level is marked with a
small left arrow.
Auto and Normal Trigger Modes
Press the trigger MENU key to display the TRIGGER menu
and press the Mode softkey to select Auto or Normal trigger
mode.
Auto mode
Use the auto trigger mode for signals other than
low-repetitive-rate signals and for unknown signal levels. To
display a DC signal, you must use Auto trigger mode since
there is no edge to trigger on.
When you press RUN/STOP key to start acquiring, the
oscilloscope first fill the pre-trigger buffer. It starts to search
for a trigger after the pre-trigger buffer is filled, and continues
to flow data through this buffer while it searches for the trigger.
While searching for the trigger, the oscilloscope overflows the
pre-trigger buffer; the first data put into the buffer is the first
pushed out. When a trigger is found, the pre-trigger buffer will
contain the events that occurred just before the trigger. If no
trigger is found, the oscilloscope generates a trigger and
displays the data as though a trigger had occurred. In this
case, the background of the Auto indicator at the top of the