In order to benchmark the quality of our magnetisation decay experimental design, fitting and interpretation, we need a reliable standard. Ideally this would be AC susceptibility, where τ mode = ⟨τ⟩ = e ⟨ln [τ]⟩ = τ Debye . However the slowest accessible AC timescale is too fast to compare to DC decay methods. Our solution is to employ the recently-proposed long-timescale AC susceptometry-like "waveform" experiment. This technique employs a low-amplitude oscillating square-wave magnetic field, that drives slow oscillations in the magnetisation, resulting in a shark-tooth-like magnetisation versus time profile (see for example Fig. ). Fourier transform of the time-domain data allows determination of the effective in-phase (χ ′ ) and out-of-phase (χ ′′ ) susceptibility components at the fundamental frequency: neglecting of the higher-order Fourier components is akin to the lock-in detection of standard regular AC susceptibility measurements. The resulting data can then be modelled in the same way as AC data (e.g. using Eq. 1). Because the magnitude of the drive field is small -Hilgar et al. proposed ± 8 Oe, and we use this magnitude hereinthe practically-accessible frequency range is order of 10 -5 -10 -1 Hz, constrained on the fast end only by the sweep rate and the discrete time taken to perform a measurement. Thus, this technique provides a bridge to benchmark the accuracy of our magnetisation decay experiments and our interpretations. We note that the waveform technique will not supplant use of magnetisation decay experiments, because it is impractical to measure enough waveform data for the slowest relaxing samples, and a single DC decay is often the most that can be measured in the instrument time available. This paper is arranged as follows: first, we determine an approximation for τ mode -1 from the SEF; second, we propose guidelines for measuring magnetisation decays; third, we compare the temperature dependence of τ Debye obtained from the waveform technique to different measures of τ extracted from magnetisation decay fits (τ * , τ mode , ⟨τ⟩ and e ⟨ln [τ]⟩ ) to determine the most accurate measure of τ for DC decay measurements, including the different variables in the fitting procedure of the SEF to the experimental data.