EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 198)

Setting Up the Instrument in Spectral Transmittance Mode
192 FTB-5240S/S-P/BP
Setting Up Spectral Transmittance Analysis Parameters
3. Under Global analysis parameters, define the following parameters
as needed:

Channel definition: indicates the limit inside which the power
values will be considered in the channel.
Centred on max peak: Channel is centered on the lowest insertion
loss peak.
ITU Grid: Select the nearest ITU channel from the peak with lowest
insertion loss.
CWDM: Select the nearest CWDM channel from the peak with
lowest insertion loss.
Custom: Channel is centered on value specified by the user.

Nominal wavelength or frequency (nm or Thz): indicates a single
value that represent the channels center wavelength (in nm) or
frequency (in THz). This field is editable only when Channel
definition is selected as Custom.