A method for calculating the mass flow rate of one or more of the phases in a multiphase flow comprising: a) Using a Coriolis meter to measure the apparent bulk density of the multiphase flow; b) Calculating a first apparent VF using the apparent bulk density from a); c) Using a microwave meter to measure the permittivity of the multiphase flow; d) Calculating a second apparent VF using the perm ittivity measurement from c); e) Calculating the phase volume fractions of the multiphase flow using the results from b) and d); f) Determining the actual bulk mass flow rate of the multiphase flow; g) Calculating the mass flow rate of one or more of the phases using the values from d) and e); wherein, in step e) a VF error curve, which correlates an apparent VF with the actual VF of a multi-phase flow, is additionally used to improve the calculation, wherein the VF error curve is generated by the method comprising: I. Using a device to measure a property of the multi-phase flow from which an apparent VF may be calculated; II. Calculating the apparent VF using the measured property from the device; III. Determining the actual VF of the multiphase flow using a radiometric densitometer; IV. Using the values from II and III to calculate the VF error; V. Repeating I - IV for all expected flow conditions to generate a VF error curve; wherein if the device is a Coriolis meter, then the measured property is the apparent bulk density of the multiphase flow; and wherein if the device is a microwave meter, then the measured property is the permittivity of the multiphase flow. a) Using a Coriolis meter to measure the apparent bulk density of the multiphase flow; b) Calculating a first apparent VF using the apparent bulk density from a); c) Using a microwave meter to measure the permittivity of the multiphase flow; d) Calculating a second apparent VF using the perm ittivity measurement from c); e) Calculating the phase volume fractions of the multiphase flow using the results from b) and d); f) Determining the actual bulk mass flow rate of the multiphase flow; g) Calculating the mass flow rate of one or more of the phases using the values from d) and e); wherein, in step e) a VF error curve, which correlates an apparent VF with the actual VF of a multi-phase flow, is additionally used to improve the calculation, wherein the VF error curve is generated by the method comprising: I. Using a device to measure a property of the multi-phase flow from which an apparent VF may be calculated; II. Calculating the apparent VF using the measured property from the device; III. Determining the actual VF of the multiphase flow using a radiometric densitometer; IV. Using the values from II and III to calculate the VF error; V. Repeating I - IV for all expected flow conditions to generate a VF error curve; I. Using a device to measure a property of the multi-phase flow from which an apparent VF may be calculated; II. Calculating the apparent VF using the measured property from the device; III. Determining the actual VF of the multiphase flow using a radiometric densitometer; IV. Using the values from II and III to calculate the VF error; V. Repeating I - IV for all expected flow conditions to generate a VF error curve; wherein if the device is a Coriolis meter, then the measured property is the apparent bulk density of the multiphase flow; and wherein if the device is a microwave meter, then the measured property is the permittivity of the multiphase flow.