Abstract: An apparatus and method for use in the quantitative analysis of blood or a similar fluid suspension. The fluid suspension is spun about a central spin axis in a chamber which circumscribes the central spin axis and whose volume varies geometrically as it extends away from the central spin axis. A fluid sample in the chamber is allowed to separate into bands or rings circumscribing the central spin axis, with the radial extent of those rings being geometrically proportional to the volume of the components. The radial extent of those bands or rings can then be used to determine the relative amounts of the components of the fluid suspension in the chamber.