Relatedly, the mean time series for T4L drifts from ≈ 3.5 to 4.0 kcal mol -1 between 10 and 30 ns, in the opposite direction to the apparent initial transient. This appeared to violate our assumption of no drift in this region and produced a long-tailed autocovariance function (Figure and Table ). However, it does not matter if this does not match the "true", infinite sampling autocovariance function for T4L, because the autocovariance function appears realistic: it shows a fast initial decay followed by long, approximately exponential tail (Figure ).