HP 8712ET User Manual page 239

Response & Isolation
This method of calibration is only necessary when trying to achieve
maximum dynamic range (>100 dB). A response and isolation calibration
prompts you to connect loads to both ports and then to connect a through
cable. These standards are measured across the frequency band you have
defined, using the number of points you have defined. These
measurements are used to remove systematic errors caused by frequency
response and crosstalk.
Enhanced Response
This method of calibration is superior to the standard response
calibration. This calibration prompts you to connect four measurement
standards: an open, a short, a load, and a through cable. The analyzer
measures each standard across the frequency band you have defined,
using the number of points you have defined. The measurements of these
standards are used to remove systematic errors caused by frequency
response and source match.
Transmission Calibration Interpolation
Widening the frequency span after performing any of these calibrations
will invalidate them, and restore the default calibration. You may
narrow the span and the analyzer will interpolate between calibration
points for the narrower span.
Note that after you have calibrated, a "C" appears in the upper right
hand corner of the display. This "C" indicates that a user-defined cal is in
use. If you change to a narrower span, note that the "C" changes to "C?",
indicating the analyzer is now interpolating between calibrated
measurement points. The "C?" notation also appears when other system
parameters, such as power, number of points, or sweep time, have
changed.
ET User's Guide
Calibrating for Increased Measurement Accuracy
Calibration Choices
6-13