Centrifuges are important tools. They can be classified by size (desktop or floor-standing), purpose (analytical or preparative) and speed (clinical, high-speed, ultra). For industrial purposes, flow-through centrifuges are available. Different kinds of rotors are available for different purposes. Centrifugation can separate by density (isopycnic) or size and shape (rate zonal). Digital data acquisition and specialised software are increasingly important to determine size, shape and interactions of macromolecules.