Characterization of sensitivity to finite perturbations

We introduce a scale dependent stability number which describes the respons e of a dynamical system to finite size perturbations. By construction, it c onverges to the maximal Lyapunov exponent in the limit of infinitesimal per turbations. We discuss different dynamical systems which are linearly stabl e but unstable in terms of the finite size analysis. In such a situation ty pical trajectories can show temporal disorder, which has its origin in a ki nd of mixing on the mesoscopic scales.