EXFO FTB-700 for FTB-1 - Manual (Page 141)

Analyzing Traces and Events
OTDR 133
Viewing and Modifying Current Trace Settings
If you already know the IOR value, you can enter it in the
corresponding box. However, if you prefer to let the application
calculate the IOR value as a function of the distance between span
start and span end, press Set IOR by Distance, then enter the distance
value.
4. If you want to save the modified IOR, RBS, and helix Factor values for
the next acquisitions performed at the current wavelength, select the
Save these settings for next acquisitions check box.
5. Press OK to apply the changes.
You return to the main window.