Flutter of turbine blades may be a reason of blade damage. Appearance of power steam turbines last stages shrouded blades flutter, realized with disk natural forms and in-phase natural forms, was registered in service by help of discrete-phase method modern variant. In this paper peculiarities of power steam turbines last stages shrouded blades flutter, realized in service with in-phase natural forms, are considered. Advantages and defects of registration of these natural forms with help of modern variant discrete-phase method induction gauges are studied. Appearance of additional errors during registration of flutter, realized with in-phase natural forms, is marked. These additional errors are called because of torsion and longitudinal vibration of turbine and generator rotors assembly and axial vibration of stator details, in which induction gauges are fastened. Measures, concerning of errors reduction, are recommended.