Greenlee 560XL Manuel D'instructions page 22

One Test Jumper Method: Connector Loss (cont'd)
2. Ensure that the light source is in continuous wave (CW) output mode.
Set the optical power meter to the appropriate wavelength (using the
[l] key) and to dBm units (using the [dB/dBm] key). Note that the dBm
output of the reference cable should be within acceptable limits.
3. To store the reference level, press the [dB/dBm] key on the optical
power meter until the "r" annunciator appears on the LCD screen (about
3 seconds). The display should read 0.00 dB. See below.
22
Press the
[dB/dBm]
key to set the
0 dB reference