That the rmsd is small (compared with the noise of data acquisition) is a necessary but not sufficient condition for the algorithm to be useful in modeling experimental data. In fact, the majority of points of the predicted concentration profiles typically fall into the plateau regions, which are trivial to predict (those in the solvent plateau are constant zero) but have limited or no information about the sedimentation process. These plateau points can keep the overall rmsd error of the solution below the statistical errors of the data acquisition, even though the maximum errors in the sedimentation boundaries may be much larger.