Effects of the undersampling of the input spectroscopic catalogue on the results of the SG method. The figure shows the percentages of substructures in the total reference cluster sample (versus the spectroscopic catalogue completeness percentage) for which the mass estimates are plagued by an error of less than X% (compared with the 100% complete spectroscopic catalogue). Blue lines are for X = 20%, green lines for X = 50%, and red lines for X = 100%. Continuous and dashed lines respectively correspond to substructures that merged and that did not merge with other substructures during the spectroscopic catalogue resampling process.