H ISTORICALLY, there has been intense and longstanding interest in the de-termination of particle size distributions, going back to the first description of the AUC by Svedberg and early applications [113, 171, 172]. Formal definitions of different distribution functions, including both sedimentation coefficient and molar mass distributions, can be found in communications from the 1950s, for example, by Williams, van Holde, Baldwin, and Fujita [111,173,174] and Gosting [175], who had embarked on the expansion of analytical approximations of the Lamm equation solutions to distributions, in largely theoretical work. Practical approaches were devised by several authors [110, 146], for example, via extrapolation schemes to address the problem of diffusion [110-112, 117, 146, 173, 175, 176]. Some of these methods were very sophisticated, but without the ability of solving the Lamm equation and fitting integral equations, they were based on concepts quite different from the modern ones.