Analytical ultracentrifugation

In this method, the sample is continuously centrifuged and an absorption profile of the result is acquired[@mitra2009Chapter 10 - Using Analytical Ultracentrifugation (AUC) to Measure Global Conformational Changes Accompanying Equilibrium Tertiary Folding of RNA Molecules]. If this is done at given times, it is possible to calculate the sedimentation velocity of the sample, like is shown in this image:

This method is built on first-principles, which means it does not require a specific form of calibration provided the medium in which the sample is suspended is known.