A method, comprising: exciting a vibration mode of a flow tube (130, 130'), wherein exciting the vibration mode of the flow tube (130, 130') comprises the steps of: periodically driving a first driver with a periodic signal; periodically driving a second driver with a periodic signal, wherein the first and second drivers (180L, 180R) are amplitude modulated out of phase from each other, and wherein a drive signal provided to the first and second drivers (180L, 180R) comprises a sum of N+1 independent signals; measuring the phase between a first pickoff and a second pickoff; exciting the first and second drivers (180L, 180R) with a plurality of off-resonance frequencies; inferring the effective phase between a modal response of the first driver and second driver (180L, 180R) at each of the plurality of off-resonance frequencies; generating a left eigenvector phase estimate at each of the off-resonance frequencies; determining a phase of a right eigenvector for the flow tube (130, 130'); and estimating a phase of a left eigenvector at a resonant drive frequency based on the phase estimates at the off-resonance frequencies; continually measuring the left and right eigenvector phases; and directly generating a time difference, Δt, value from the difference between the left eigenvector phase and the right eigenvector phase. exciting a vibration mode of a flow tube (130, 130'), wherein exciting the vibration mode of the flow tube (130, 130') comprises the steps of: periodically driving a first driver with a periodic signal; periodically driving a second driver with a periodic signal, wherein the first and second drivers (180L, 180R) are amplitude modulated out of phase from each other, and wherein a drive signal provided to the first and second drivers (180L, 180R) comprises a sum of N+1 independent signals; measuring the phase between a first pickoff and a second pickoff; exciting the first and second drivers (180L, 180R) with a plurality of off-resonance frequencies; inferring the effective phase between a modal response of the first driver and second driver (180L, 180R) at each of the plurality of off-resonance frequencies; generating a left eigenvector phase estimate at each of the off-resonance frequencies; determining a phase of a right eigenvector for the flow tube (130, 130'); and estimating a phase of a left eigenvector at a resonant drive frequency based on the phase estimates at the off-resonance frequencies; periodically driving a first driver with a periodic signal; periodically driving a second driver with a periodic signal, wherein the first and second drivers (180L, 180R) are amplitude modulated out of phase from each other, and wherein a drive signal provided to the first and second drivers (180L, 180R) comprises a sum of N+1 independent signals; measuring the phase between a first pickoff and a second pickoff; exciting the first and second drivers (180L, 180R) with a plurality of off-resonance frequencies; inferring the effective phase between a modal response of the first driver and second driver (180L, 180R) at each of the plurality of off-resonance frequencies; generating a left eigenvector phase estimate at each of the off-resonance frequencies; determining a phase of a right eigenvector for the flow tube (130, 130'); and estimating a phase of a left eigenvector at a resonant drive frequency based on the phase estimates at the off-resonance frequencies; continually measuring the left and right eigenvector phases; and directly generating a time difference, Δt, value from the difference between the left eigenvector phase and the right eigenvector phase.