The invention relates to the field of aerial propellers, in particular the field of variable-pitch propellers, specifically for unducted fans. When rotating a rotor 101 by three-phase drive signals U, V, and W generated based on a CLK signal from a VCO 7, induction voltages induced in the three-phase coils 102 are monitored and a phase deviation of a rotor phase relative to an electric phase is detected. The tax information may be supplied to the apparatus from a remote location, and the scanned data may be compared to the tax information supplied to the apparatus to verify that the tax indicia have been applied to the cartons of cigarettes. The first and second axes are generally orthogonal to one another and to the strut axis. The ribs provide that the inner shell can be unscrewed from a threaded core of a manufacturing mold during production without causing noticeable distortion in the closure.