Estimation of counted quantum phase

The estimation of phase shift in realistic experiments is addressed here. Provided that the phase concept is not ideal, the phase shift should always be inferred from the performed measurement. Particulary, two different estimations are suggested. The conditional probability is given by the experimentally observable dependence of the measured probability on the phase shift. As an explicit example, the accuracy of the phase measurement on the Mach-Zehnder interferometer is evaluated using different methods for comparison.