EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 267)

OSA 261
12 Managing Results
Each test mode has its own results tabs, where you can view the trace
details, channel results and global results for all measured channels.
You can use zoom options on the trace, configure markers to view the
power values for specific wavelengths, and view trace information.
You can also manage trace files and generate reports for all test modes.
Note: When a power result is flagged using an asterisk ( * ), it means that the
detector is saturated. When the optical power on the detector is too high,
the detector gets saturated and the returned value is probably incorrect.
Note: When an OSNR or a noise result is flagged using a question mark ( ? ), it
means that the quality of the result is insufficient to make a valid
calculation. This indication can be produced when analyzing an
InBand/i-InBand measurement, or when computing noise through
polynomial fit . This indication can arise in the following situations:

InBand/i-InBand averaging was made using a very few scans (1 or 2 for
example). Usually produced when the operator presses the Stop
button before the end of the InBand/i-InBand acquisition.

The data in the measured channel is subjected to fast polarization
scrambling, or is a polarization multiplexed signal.

One channel might have a misfit with the current state of the
polarization scrambler inside the module. This can be corrected by
moving the fiber at the entrance of the module.

The polarization scrambler inside the module could be defective. If
you suspect this option please contact EXFO technical support for a
more complete diagnosis.

Polynomial fit coefficient correlation is questionable.