EXFO FG-750 - Manual (Page 174)

Operating Your RTU in OTDR Measuring Mode
160 FG-750
Creating the Reference Traces
Creating the Reference Traces
Before starting the learning process, the application must create the
reference traces. The reference traces are created automatically just after a
fiber detection, after a renew, and when a test setup is added or updated.
If you modify the acquisition or analysis parameters, the application will
prompt you to perform a new reference. This reference will be
independent from the previous one. A new learning process, based on this
new reference, will also be scheduled.
It is also possible to re-create a reference trace afterwards, if you have
made a repair, for instance.