Let us imagine that the magnetization of a single superparamagnetic nanoparticle is measured and let us define formula_5 as the measurement time. If formula_6, the nanoparticle magnetization will flip several times during the measurement, then the measured magnetization will average to zero. If formula_7, the magnetization will not flip during the measurement, so the measured magnetization will be what the instantaneous magnetization was at the beginning of the measurement. In the former case, the nanoparticle will appear to be in the superparamagnetic state whereas in the latter case it will appear to be “blocked” in its initial state.