A magnetic flowmeter generates an alternating potential representing flow. A controlled current excites the flowmeter with first and second amplitudes of current. A correction output represents the first and second amplitudes. A circuit connected to the correction output and the alternating potential oscillates at a frequency representing the alternating potential corrected for variation of the first and second amplitudes. Frequencies of the oscillations at first and second amplitudes are measured. An output is calculated as a function of a subtraction of the first and second measured frequencies such that the effect of offset is reduced.