EXFO FTB-500 (Window XP) - Manual (Page 125)

Using the Optional Built-In Power Meter and VFL
FTB-500 115
Setting Reference Values on Your Power Meter
Setting Reference Values on Your Power Meter
In Reference mode, your unit displays the loss created by the fiber under
test only, since it subtracts a reference value from the measured power.
You can set a different reference value for each wavelength. A reference
value remains in memory until a new one is stored at the same
wavelength.
To set reference values to use in Reference mode:
1. Check your fibers and clean them properly.
2. Using the proper adapter and test jumpers, connect a light source to
your power meter.
3. From the Instrument View tab, select the wavelength in the list.
Activate the source at the same wavelength.
4. Tap Reference to save the current power value as the new reference. It
will appear on the upper-right corner of the data display.
Wavelength list