Itô frequency random-walk → Allan variance σ²_y(τ) ~ τ^α; α = −1 (WFM), +1 (RWFM)

Itô-stochastic-integral framework for clock frequency noise and the Allan variance — the canonical tool for characterising time-domain instability of atomic and optical frequency standards (Allan 1966; Barnes et al., IEEE Trans. IM-20,…