  Recently, oscillator-based Boolean computation has been proposed for its
potentials in noise immunity and energy efficiency. In such a system, logic
bits are encoded in the relative phases of oscillating signals and stored in
injection-locked oscillators. To show that the scheme is very general and not
specific to electronic oscillators, in this paper, we report our work on
storing a phase-based logic bit in the relative phase between two mechanical
metronomes. While the synchronization of metronomes is a classic example
showing the effects of injection locking, our work takes it one step further by
demonstrating the bistable phase in sub-harmonically injection-locked
metronomes --- a key mechanism for oscillator-based Boolean computation.
Although we do not expect to make computers with metronomes, our study
demonstrates the generality of this new computation paradigm and may inspire
its practical implementations in various fields, eg, MEMS, silicon photonics,
spintronics, synthetic biology, etc.
