EXFO FTB-7000 OTDR Series for FTB-500 - Manual (Page 348)

SCPI Command Reference
334 OTDR
Product-Specific Commands—Description
:CALCulate[1..n]:IORefraction
Description This command sets the index of refraction that
will be used for the trace corresponding to the
specified trace index.
Using this command will recalculate the event
table automatically.
*RST clears this setting.
Syntax :CALCulate[1..n]:IORefractionTRC1|TRC
2|TRC3|TRC4,