(a) S(Δt) versus time elapsed for PSR B1828−11. Each curve is for a different embedding dimension from 2–10 starting at the lowest curve. The vertical red lines mark the region where least-squares regression was applied. This corresponds to an average maximum Lyapunov exponent of λ_max = (4.0 ± 0.3) × 10^{− 4} inverse days. (b) S(Δt) for a surrogate data set for B1828−11.