HP 54600B User's And Service Manual page 24

The Oscilloscope at a Glance
To set up the time base
Turn the Delay knob and notice that its value is displayed in the status line.
The Delay knob moves the main sweep horizontally, and it pauses at
0.00 s, mimicking a mechanical detent. At the top of the graticule is a
solid triangle ( ) symbol and an open triangle
( ) symbol. The symbol indicates the trigger point and it moves
in conjunction with the Delay knob. The symbol indicates the time
reference point. If the time reference softkey is set to left, the is
located one graticule in from the left side of the display. If the time
reference softkey is set to center, the is located at the center of the
display. The delay number tells you how far the reference point is
located from the trigger point .
All events displayed left of the trigger point happened before the
trigger occurred, and these events are called pretrigger information.
You will find this feature very useful because you can now see the
events that led up to the trigger point. Everything to the right of the
trigger point is called posttrigger information. The amount of delay
range (pretrigger and posttrigger information) available is dependent
on the sweep speed selected. See "Horizontal System" in chapter 5 for
more details.
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