The accuracy of the description of the shape of the sedimentation boundary (rather than the plateaus) is critical for modeling the size-and-shape distributions. Therefore, a sufficient condition is that the maximum error is smaller than the noise of the data acquisition. For example, in order to model experimental data with signal-to-noise ratio of up to *1000:1, the maximum errors of the Lamm equation solutions at unit concentration should be less than 0.001.