HP 54710A User's Reference Manual page 349

Limit Test Menu
Fail When
Never Fail never sets the oscilloscope so that a measurement never fails
on a test. Use the fail never mode when you want to observe one
measurement but determine a failure from a different measurement.
The fail never mode allows you to monitor a measurement without having to
set up any fail criteria.
Measurement Not Found
The Meas not found softkey allows you to determine what action the limit
test takes when the oscilloscope cannot perform a measurement. For
example, if the oscilloscope cannot find an edge on a rise time measurement,
what action should the limit test take?
If the oscilloscope is stopped, you can cycle through the measurement not
found selections to see the limit test results in more detail.
Fail Fail is used in cases where the instrument cannot make a
measurement. For example, when an edge is expected to be present but
is not found. The fail mode is used for most applications.
The total number of waveforms is incremented, and the total number of
failures is incremented.
Pass You might use the pass parameter when triggering on one event
and measuring another event that may not occur on every trigger. For
example, in a communications system, you may want to trigger on the
clock and test the rise times of edges in the data stream. However, there
may be no way to guarantee that a rising edge is present to measure in
the data stream at every clock edge. By using the pass parameter, the
limit test will not log a failure if an edge is not found in the data stream.
If the measurement cannot be made, then the total number of waveforms
measured is incremented, but the total number of failures is not incremented.
Ignore Ignore is similar to Pass, except that the totals for the number of
waveforms and failures are not incremented. Therefore, the total
indicates the number of tests when the measurement was available.
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