Joinwit JW3213 Series User Manual page 17

display relative value (dB), see as following:
In order to get the loss between the two measurements, do another time
testing under the first relative output power. The relative value will be
calculated automatically. For example the second time testing of 1310nm
output power is -35dBm, the relative output power will be -15dBm.(relative
output power=absolute output power-reference value -15dBm=-35.00dBm-
（-20.00dBm） see as following:
After finishing testing, cover the dusty cap to keep the optical connector
port to be clean.
⑤：JW3213&JW3213AVwithout this function.
⑥
VFL module
During the event or break point checking of the short distance optic fiber
and pigtails we can use the VFL function.
First of all, Clean the optic Fiber end-face, and connect it them the VFL
port (FC adaptor), after open the instruments, press "
function, then can see the visual laser at the breaking point or the end of the
pigtails. Press "
1 6
" to shift the CW and the Hz wavelength. And press
Ref
Absolute value
Relative value
" to activate this