  It has been known that several objects such as cluster variables,
coefficients, seeds, and $Y$-seeds in different cluster patterns with common
exchange matrices share the same periodicity under mutations. We call it
synchronicity phenomenon in cluster patterns. In this expository note we
explain the mechanism of synchronicity based on several fundamental results on
cluster algebra theory such as separation formulas, sign-coherence, Laurent
positivity, duality, and detropicalization obtained by several authors. We also
show that all synchronicity properties studied in this paper are naturally
extended to cluster patterns of generalized cluster algebras, up to the Laurent
positivity conjecture.
