What kind of calibration is required?

If only flow rate is needed, we can measure such without any input data.

If water cut is to be measured in addition to flow rate, we need to measure Speed of Sound (SoS) of a sample of pure oil and water plus temperature and salinity of water is required. Xsens have handheld SoS measurement cells available so we can do this one-time SoS measurement in the field.