EXFO FTB-7000 OTDR Series for FTB-500 - Manual (Page 260)

Analyzing Bidirectional Traces
246 OTDR
Viewing and Modifying Current Trace Parameters
To modify the current trace settings:
1. From the main window, press the A->B Info or B->A Info button then
press the Edit Current Trace Settings button.
2. Enter values for the current trace in the appropriate boxes.
OR
Revert to default values by pressing the Default button.
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 function of the distance between span start
and span end, press Set IOR by Distance, then enter the distance
value.