EXFO IQS-1700 High Performance Power Meter for IQS-500/600 - Manual (Page 49)

Preparing Your High Performance Power Meter for a Test
High Performance Power Meter 41
Nulling Offsets
To perform an offset nulling on all channels (two- and
four-channel power meters):
1. Install the protective caps over all of the detector ports.
2. Under Nulling, click the All Channels button.
Offset nulling values are applied to the channel until a new nulling is
performed. A message prompts you to ensure that the detector caps
are properly installed.