HP 54710A User's Reference Manual page 60

Front-Panel Features
Indicator Lights
When the oscilloscope is externally triggered, there is no such indicator.
However, you can use the triggered light to help you determine the trigger
thresholds. To do this, simply move the trigger level in either direction.
When the triggered light turns off, you know that is one of the trigger
thresholds. Move the trigger level in the other direction to determine the
other threshold. You now know what the trigger thresholds are and you can
set the trigger level accordingly for your application. Typically you set the
trigger level half way between the two thresholds.
Auto Triggered
When the auto triggered light is on, it indicates that the oscilloscope is not
seeing any valid trigger events, and that the oscilloscope is forcing itself to
trigger every 30 ms.
If you see that the auto triggered light is on, you know that the oscilloscope is
triggering and that the screen should display data. If the screen is not
displaying data, check the channel offset to see if it is set correctly, and
check to make sure that the channel display is turned on. If you are using
both single-wide and two-wide plug-ins and the memory depth is set to
greater than 16K, check the time base position setting.
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