Left panel: stacked histogram of the errors made by the visual time-delay estimation, for the secure and plausible D3CS samples. All the secure estimations are within the displayed range of errors of ± 20 days. Only 2.6% of the time delays in the plausible sample have an absolute error larger than 20 days. Right panel: absolute time-delay error made by D3CS as a function of the true delay for both samples.