The final option is the choice of the most appropriate measure of τ to replicate τ Debye as closely as possible (Fig. ). It is clear that e ⟨ln [τ]⟩ is consistently in the best agreement with τ Debye across the whole temperature range, and therefore we contend that e ⟨ln [τ]⟩ should be used as the experimental definition of the magnetic relaxation time for the SEF in conjunction with magnetisation decay experiments.