EXFO OTDR 2 - Manual (Page 34)

Preparing Your OTDR for a Test
26 OTDR
Setting the IOR, RBS Coefficient, and Helix Factor
4. From the Wavelength list, select the desired wavelength.
Note: The helix factor value takes into account the difference between the length
of the cable and the length of the fiber inside the cable; it does not vary with
wavelengths. For this reason, you cannot define a different helix factor for
each wavelength.
I
MPORTANT
Change the default RBS coefficient only if you have values provided
by the fiber manufacturer. If you set this parameter incorrectly, your
reflectance measurements will be inaccurate.
Wavelength for which
RBS and IOR will be
defined
The Revert to Factory Settings
button resets all the values in
the Link Definition tab