EXFO FTB-5230S Optical Spectrum Analyzer for FTB 200 v2 - Manual (Page 129)

Setting Up the Instrument in Drift Mode
OSA/OCA 123
Setting Up Drift Analysis Parameters
4. Enter values in the boxes as explained below:

Wavelength/Frequency (nm/GHz): central wavelength/frequency
of the channel.

Signal power (dBm): signal power for the selected channel
(excludes noise).

OSNR (dB): Optical Signal to Noise Ratio, given by Signal power
(according to the current calculation method, in dBm) minus
Noise (according to the current calculation method, in dBm).
5. Press OK to save the changes and close the window, or press Cancel to
exit without saving.
Press Restore Defaults to remove all the changes and apply the default
values.