a measuring tube, which is excited to oscillate during a measurement operation and through which a liquid flows, the mass flow of which is to be measured;

first and second sensors for registering a mass-flow-dependent oscillation of said measuring tube and for producing first and second sensor signals;

at least one reference signal generator, which superimposes on said first and second sensor signals one and the same reference signal;

a first input branch for conditioning a first auxiliary signal formed from said first sensor signal and said superimposed reference signal;

a second input branch for conditioning a second auxiliary signal formed from said second sensor signal and said superimposed reference signal;

means serving for filtering from said conditioned first auxiliary signal a conditioned first sensor signal and a conditioned first reference signal;

means serving for filtering from said conditioned second auxiliary signal a conditioned second sensor signal and a conditioned second reference signal;

means for determining one of: a phase difference and a travel-time difference between said first, conditioned, reference signal and said second, conditioned, reference signal; and for either correcting the phase difference between said first and second, conditioned, sensor signals on the basis of said phase difference between said first, conditioned, reference signal and said second, conditioned, reference signal or for correcting the travel-time difference between said first and second conditioned sensor signals on the basis of said travel-time difference between said first conditioned reference signal and said second conditioned reference signal; and for determining the mass flow on the basis of the corrected, conditioned, sensor signals.