The AUC is a high speed centrifuge with an optical system that allows the user to observe the sedimentation process in real time. 

Several types ofoptical system are available for observation of the concentration of macromolecules as a function of radius and time. There are two basic modes of operating the ultracentrifuge: velocity mode and equilibrium mode. In the equilibrium mode, relatively low speeds are used such that a an exponential gradient of macromolecule is allowed to build up with sedimentation proceeding until it is opposed by diffusion so that no further concentration changes occur. When the system is at equilibrium, the radial dependence of the concentration distribution is determined be the molar mass distribution. Appropriate analysis of the concentration gradient allows determination of molar mass, stoichiometry and equilibrium constants for interacting sand non-interacting systems. The second mode is the velocity mode in which a relatively high speed is employed so that a distinct boundary is formed between the sedimenting macromolecule and the buffer left behind.