For accurate results, the instrument must be calibrated before making any 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. Unless the calibration type is Flexcal, the instrument must also be re-calibrated every time the setup frequency changes.

The instrument can be manually calibrated with a precision OSL (Open-Short-Load) calibration tee / discrete components or with the InstaCal module. The benefit of the InstaCal module is that it is much faster, requires no connection changes, and eliminates the need to use three different terminations (open, short, load) for calibration. The trade-off is that the specified corrected directivity is 38 dB instead of 42 dB.

While InstaCal or OSL Cal tee provides two alternatives for the tools needed to perform the calibration, Standard Cal or FlexCal determines how often calibration will need to be performed. A standard calibration is an Open, Short and Load calibration for a selected frequency range, and is no longer valid if the frequency is changed. The default calibration mode is standard.

FlexCal is a broadband frequency calibration that remains valid if the frequency is changed.

Flexcal calibrates the instrument over the entire frequency range and interpolates datapoints if the frequency range is changed. This method saves time as it does not require the user to re-calibrate the system for frequency changes. The trade-off is that the accuracy is not the same as it would be with the standard calibration. It is recommended for troubleshooting purposes. Table: Summary of Calibration Methods and Tools has a summary of calibration methods and tools.