EXFO FTB-7000 OTDR for FTB-200 v2 - Manual (Page 185)

Analyzing the Results Manually
OTDR 171
Getting Event Loss (Four-Point and Least-Square Approximation)
5. Position marker B at the beginning of the linear area following the
event to be measured.
6. Position submarker b at the end of the linear area following the event
to be measured (must not include any significant events).
Note: The loss values that are displayed depend on which calculation methods
are selected (see Selecting the Attenuation and Loss Values that Will Be
Displayed on page 163).
4
3
5
6
Event to be measured
Linear area
Linear area
Least-square
approximation Four-point event loss
from the areas delimited
by markers
a, A, B and b