EXFO FTB-700 for FTB-1 - Manual (Page 283)

Maintenance
OTDR 275
Verifying Your OTDR
2. Set the distance range to 80 km (singlemode fiber), the pulse width to
the longest value available and the acquisition time to 180 seconds.
The measurement range using the non-reflective event method
represents the amount of attenuation (dB) between the launch level
and a 0.5 dB splice (which can be detected and measured to an
accuracy of ± 0.1 dB). You can measure it by simply making an
acquisition on a fiber with a known attenuation and a known 0.5 dB
splice. Attenuation between the splice and the launch level is added
until the analysis can no longer measure the splice to within ± 0.1 dB.