EXFO IQS-1500 Power Meters for IQS-500/600 - Manual (Page 43)

Measuring Power
Power Meters 35
Measuring Relative Power
Measuring Relative Power
Power measurements can be displayed as a deviation from an absolute
reference value. The relative power is particularly useful when performing
loss measurements.
Relative power is displayed in dB when the reference value is measured in
dBm. In this case, the value will be either positive or negative, as the actual
measured power is higher or lower than the reference power.
If the reference value is in W, the relative power will be displayed in W/W.
In this case, the relative power is the deviation ratio from the reference and
will always be a positive value (unless operation was improperly done).
To display significant relative power values, it is important to have an
appropriate reference value, which you activate by clicking the Reference
button in the Instrument function tab.