HP 54710A User's Reference Manual page 295

Trigger Menu
Mode
Delay events
Delay by events has the oscilloscope arm on an edge from one of the channel
or trigger inputs, wait for a number of events that you specify in the menu,
then trigger on an edge from any of the other channel or trigger inputs.
Basically you can think of delay by events as two edge triggers that are
separated by a selectable number of events. You can arm the trigger circuit
on one slot, count events on a second slot, then trigger on a third slot.
You can use delay by events for reducing the jitter on long delay
measurements on a pulse burst or pulse train. If you use a long time base
delay to look at a particular pulse in a pulse burst or pulse train, the jitter on
the pulse can make it almost impossible to see the desired pulse. Delay by
events allows you to delay out to the pulse of interest, then trigger on that
pulse. Because you are triggering on the pulse of interest, jitter is not a
factor in viewing the pulse.
For example, you may want to look at the 97th pulse out of 100 pulses. You
can arm on the first pulse, then delay out 95 events, then trigger on the 97th
pulse. By varying the number of events, you can consecutively look at pulses
before and after the pulse of interest.
Arm on Selects the slot, trigger level, and slope for the arming
conditions of the trigger circuitry.
Event Selects the slot, trigger level, and slope for the event the trigger
circuitry is to count.
Delay Used to set the number of events to count from 0 to 16 million.
Trigger Selects the slot, trigger level, and slope for the trigger event.
18–16