EXFO FTB-500 (Window XP) - Manual (Page 117)

FTB-500 107
6 Using the Optional Built-In
Power Meter and VFL
The FTB-500 can be equipped with an optical power meter to measure
absolute power (dBm or W) or insertion loss (dB). The power meter can
detect modulated signals (1 kHz, 2 kHz, and 270 Hz).
The FTB-500 can also include a visual fault locator (VFL) to inspect or
identify fibers.
I
MPORTANT
If you intend to take measurements with a very low power level,
make sure that your testing conditions are optimal to ensure the
best results (for example, do not use the VFL, make sure that the
other modules in your platform are not performing measurements
and that their internal parts are not moving, etc.).