EXFO IQS-12002B Calibration System - Manual (Page 82)

Calibration Methods
78 IQS-12002B
FTB-7000D and FTB-7000B-B OTDR Modules
Event Dead Zone
The event dead zone is the distance between markers A and B on the
OTDR trace presented below.
Markers are positioned on both side of the peak, 1.5 dB below the
maximum peak value.
Dead zone