HP 8712ET User Manual page 260

Calibrating for Increased Measurement Accuracy
Checking the Calibration
Figure 6-6
All other calibration types do not correct for source
match. The source match error term for other types of
calibrations will be equal to the raw source match of
the port in these cases. See
This value can be in the −22 dB range.
6-34
Typical Source Match (Corrected) Error Term
Figure 6-7.
ET User's Guide