A system for validating a mass flow calibration factor of a Coriolis flowmeter having: flow tube means (103A-B); driver means for oscillating said flow tube means as a material flows therethrough, the material having a known density or density constant; sensor means (105-105') for detecting oscillation of said flow tube means (103A-B); a memory for storing said known density or density constant; and processor means arranged to: determine a measured period of oscillation of said flow tube means (103A-B) from signals received from the sensor means (105-105'); and at least one of: compare the measured period of oscillation with an expected period of oscillation, the expected period of oscillation being determined from said known density of said material; or determined a measured density or density constant of the material from the measured period of oscillation and compare the measured density or density constant with the known density or density constant; and signal that a possible error condition in mass flow calibration factor exists in dependence on the comparison, the mass flow calibration factor being the ratio of: the mass flow rate of the material along the tube; and the oscillation phase difference at two different points along the tube. flow tube means (103A-B); driver means for oscillating said flow tube means as a material flows therethrough, the material having a known density or density constant; sensor means (105-105') for detecting oscillation of said flow tube means (103A-B); a memory for storing said known density or density constant; and processor means arranged to: determine a measured period of oscillation of said flow tube means (103A-B) from signals received from the sensor means (105-105'); and at least one of: compare the measured period of oscillation with an expected period of oscillation, the expected period of oscillation being determined from said known density of said material; or determined a measured density or density constant of the material from the measured period of oscillation and compare the measured density or density constant with the known density or density constant; and signal that a possible error condition in mass flow calibration factor exists in dependence on the comparison, the mass flow calibration factor being the ratio of: the mass flow rate of the material along the tube; and the oscillation phase difference at two different points along the tube. determine a measured period of oscillation of said flow tube means (103A-B) from signals received from the sensor means (105-105'); and at least one of: compare the measured period of oscillation with an expected period of oscillation, the expected period of oscillation being determined from said known density of said material; or determined a measured density or density constant of the material from the measured period of oscillation and compare the measured density or density constant with the known density or density constant; and signal that a possible error condition in mass flow calibration factor exists in dependence on the comparison, the mass flow calibration factor being the ratio of: the mass flow rate of the material along the tube; and the oscillation phase difference at two different points along the tube. compare the measured period of oscillation with an expected period of oscillation, the expected period of oscillation being determined from said known density of said material; or determined a measured density or density constant of the material from the measured period of oscillation and compare the measured density or density constant with the known density or density constant; and signal that a possible error condition in mass flow calibration factor exists in dependence on the comparison, the mass flow calibration factor being the ratio of: the mass flow rate of the material along the tube; and the oscillation phase difference at two different points along the tube. the mass flow rate of the material along the tube; and the oscillation phase difference at two different points along the tube.