An apparatus comprising a classification block, a pattern generator block, a hash key block and a replacement block. A scale practice device is fixed to a musical instrument, a tone generated by the musical instrument is collected as a mechanical vibration, and tuning results are calculated. A ring gear wraps around each set of planetary gears so that the internal perimeter of the ring gear is meshed with each of the planetary gears in the set. Optionally, when the first and second sensed signals are both representative of the potential failure, the method further includes determining whether the first and second sensed signals are correlated with one another.