Agilent Technologies N1996A-503 User Reference page 341

Questionable Status Register
The questionable status register monitors the instrument's condition to see if anything
questionable has happened to it. It is looking for anything that might cause an error or a
bad measurement like a hardware problem, an out of calibration situation, or a unusual
signal. All the bits are summary bits from lower-level event registers.
Bit Condition
5 Frequency summary
9 Integrity summary
Chapter 6
Operation
The instrument hardware has detected an unlocked
condition or a problem with the external frequency
reference.
The instrument hardware has detected a signal
integrity problem. The signal amplitude may be too
high.
Using The Status Monitoring Subsystem
Questionable Status Register
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