KEYSIGHT's N9913A-211 option 210 provides transmission/reflection or S21 and S11 measurement capabilities, along with one-port and enhanced response calibrations. To obtain all four S-parameters—forward and reverse (S11, S21, S12, S22) and full two-port calibration—option 211 should be ordered. Full two-port calibration is the most accurate calibration available with FieldFox network analyzers. br brOption 210 is a prerequisite for option 211. So you must order option 210 if you want option 211. br br *Must be ordered with mainframe. Drop ship only.