Finally, two cases in which this effect may be significant are: (1) if the structure is undergoing a transient perturbation, e.g. the triangle perturbation of Fig. 2 , in which case measurements of the perturbation timescale cannot be completely relied upon to determine Ω ref ; and (2) if the structure nominally undergoes sinusoid motion but then this waveform is altered, e.g. an insect flight motor during an extreme manoeuvre (see Gau et al., 2021) .
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