2-Port Transmission Measurement Guide : 2-port Transmission Measurement (Option 21) : Calibration
 
Calibration
For accurate results, the instrument must be calibrated before making 2-port measurements. The instrument must be re-calibrated whenever the temperature exceeds the calibration temperature range or when the test port extension cable is removed or replaced. The instrument must also be re-calibrated every time the setup frequency changes.
2-port Calibration