The 2DSA algorithm applied by the Demeler laboratory consists of a large number of repeated applications of Eq. (4) with K & 10 9 10 and similarly low-resolution grids. Figure 3 shows the results of fitting the same data as shown in Fig. 1 with a 10 9 10 grid under otherwise identical conditions. The deviations are ±10% of the maximum signal, and clearly this model does not even qualitatively describe the data well. As a consequence, we cannot assume that the distribution obtained from this model reflects in any way the species present in the experiment. (It is grossly different, for example, from the distribution shown in Fig. 1c, d. ) Brookes et al. (2009) recognize that such a fit is insufficient and consistently attribute the idea of using 10 9 10 grids to Brown and Schuck. For example, the authors state ''…a 10 9 10 grid as proposed by Brown and Schuck a Experimental data, with the color temperature blue to red indicating the temporal evolution of the sedimentation, as in Fig. 1 . Shown as black lines are the best-fit distributions with the 10 9 10 grid distribution model, ranging from f r -values of 1.0 to 2.5 in ten equidistant steps, and from s-values of 0.1 to 15.0 S in ten equidistant steps. b Residuals bitmap and overlay. The rmsd of the fit is 0.03088 OD. c Best-fit size-and-shape distribution with the 10 9 10 model, in the same presentation as the 10 9 100 model in Fig. 1c Fig . 2 Accuracy of the solution of the Lamm equation. Whenever using linear elements for the finite-element solution, an obligatory error is the approximation of the true boundary shape by piecewise linear segments. This is illustrated here for a system chosen as model system by Cao and Demeler (2005, compare Fig. 8b) , with s = 10 S and D = 2 9 10 -7 cm 2 /s, for which very accurate Lamm equation solutions were calculated with a very fine discretization (black thin line). If the radial range from meniscus to bottom is divided evenly in a set of only 100 radial points and the boundary shape is approximated by piecewise linear segments (red line, residuals shown in enhanced scale in the graph below), very large deviations occur, even if at these points the correct Lamm equation solutions were calculated. For an even division with 200 radial points (blue) the obligatory errors are smaller but still approximately ten times the experimental noise. Grids with 100 radial points were proposed by Cao and Demeler (2005) , leading for samples at unit concentration to maximum errors far exceeding the experimental noise. As shown by Brown and Schuck (2008) , the minimum number of radial points that for this system allow for this obligate error to be \0.001 is *300, based on an optimized nonequidistant spacing of radial points (using high density where boundaries are steep) (2006) is insufficient to reliably describe the experimental parameter space. If the actual solute is not aligned with a grid point, false positives are produced,'' and even declare the second major point in their results as ''A 10 9 10 grid suggested by Brown and Schuck (2006) is clearly insuffi-cient…,'' and state in the summary ''We have shown that low resolution grids as proposed by Brown and Schuck (2006) are insufficient to obtain reliable information.'' This attribution is not based on reality. Unmistakably, we have used in the referenced work (Brown and Schuck 2006) exclusively high-resolution grids (11 9 100 in Fig. 1 and 2, 12 9 60 in Fig. 3, 15 9 50 in Fig. 4, 13 9 100 in Fig. 5, 11 9 100 in Fig. 6 , and finally 13 9 50 in Fig. 7) , all of which are shown to describe the data well to within the noise of data acquisition (Brown and Schuck 2006) , and similar is true for other published applications of the method by other laboratories and by us. Thus, the idea of using 10 9 10 grids is entirely a product of the Demeler laboratory, and, to our knowledge, first described in the Brookes et al. (2009) paper.