where Γ is the Gamma function and Eu = 0.5772... is the Euler constant. When the distribution of relaxation times is large (i.e. β is small for the SEF, or α is large for the Generalised Debye model), the concept of "the relaxation time" τ begins to lose physical meaning. However, even at relatively high values of β , the different measures of τ for the SEF diverge (Fig. ). The expectation value ⟨τ⟩ is always longer than τ * , while e ⟨ln [τ]⟩ is always shorter than τ * and both rapidly diverge from τ * at β < 0.5. The value of τ mode is also larger than τ * , but goes through a maximum at β ≈ 0.4, where τ mode is approximately twice as large as τ * (Fig. ). The staggering difference in β -dependence for the different measures of τ is likely to have significant implications on the temperature-dependence of magnetic relaxation rates, as β values commonly vary with temperature; this could have important consequences for the accurate chemical interpretation of relaxation dynamics. 3 Experimental Details