As I previously mentioned I used a Dynavibe to balance my prop. One thing that was confusing at first was that the phase angle changed with rpm. After thinking about it, that is what is likely to happen. The engine, it?s mounts, and prop is a mechanical system consisting of mass (the engine), a spring force ( rubber mounts) damping (rubber mounts also), and driving force ( prop imbalance). That is a classic driven spring-mass-damped system, which is mathematically well known. This system has a resonant frequency. Resonance occurs at a phase angle of 0. As we change rpm, and go off resonance, the phase angle will change, either leading or lagging, depending on whether + or - rpm change. We don?t necessarily operate at resonance anywhere in the normal rpm range. Hopefully not! I never saw a phase angle near 0. This is a phenomenon studied in engineering and the math that goes along with it. Things are probably more complex than this since there are multiple driving forces (engine pulses, aerodynamic effects). But at least the varying phase has an explanation.