An electromagnetic flowmeter assembly comprising: one or more excitation coils for generating an excitation field across a flow conduit; excitation circuitry for generating an excitation signal for application to the one or more excitation coils; one or more electrodes for sensing the electromagnetic field generated across the flow conduit as a result of interaction between the excitation field and fluid flowing along the flow conduit; processing circuitry (10,12) for processing signals obtained from the one or more electrodes to determine one or more flow measurement values indicative of the fluid flow through the conduit; characterized in that the processing circuitry (10,12) comprises a calibration data store for storing gain calibration data relating to the gains of circuit components of the processing circuitry and is operable to determine said one or more flow measurement values using said signals obtained from said one or more electrodes and said gain calibration data; said processing circuitry (10,12) is operable to combine said calibration data with said signals obtained from the one or more electrodes to correct for gain characteristics of the components of the processing circuitry; said processing circuitry (10,12) is operable to calibrate an analogue to digital converter of the processing circuitry against a reference source to obtain gain calibration data for the analogue to digital converter, and is operable to use the calibrated analogue to digital converter to calibrate one or more amplifiers of the processing circuitry; and the processing circuitry further comprises means for dynamically updating said gain calibration data. one or more excitation coils for generating an excitation field across a flow conduit; excitation circuitry for generating an excitation signal for application to the one or more excitation coils; one or more electrodes for sensing the electromagnetic field generated across the flow conduit as a result of interaction between the excitation field and fluid flowing along the flow conduit; processing circuitry (10,12) for processing signals obtained from the one or more electrodes to determine one or more flow measurement values indicative of the fluid flow through the conduit; characterized in that the processing circuitry (10,12) comprises a calibration data store for storing gain calibration data relating to the gains of circuit components of the processing circuitry and is operable to determine said one or more flow measurement values using said signals obtained from said one or more electrodes and said gain calibration data; said processing circuitry (10,12) is operable to combine said calibration data with said signals obtained from the one or more electrodes to correct for gain characteristics of the components of the processing circuitry; said processing circuitry (10,12) is operable to calibrate an analogue to digital converter of the processing circuitry against a reference source to obtain gain calibration data for the analogue to digital converter, and is operable to use the calibrated analogue to digital converter to calibrate one or more amplifiers of the processing circuitry; and the processing circuitry further comprises means for dynamically updating said gain calibration data.