Abstract: A rotatable element for use in centrifugal chemical-medical analysis apparatus wherein inlet means is provided in the element near the center of rotation thereof and an outlet is provided near the marginal radially outward edge thereof. A measuring chamber is provided intermediate the inlet and outlet and a conduit is afforded to such chamber from the inlet. A passageway is provided in the element extending radially inwardly from the chamber to a predetermined point or position relative to such chamber, and then to an overflow outlet to thereby define a predetermined filling level for the chamber.Fluid entering the inlet of the rotating element flows simultaneously into the chamber and the passageway under the centrifugal force, the fluid at said predetermined point relative to said measuring chamber overflowing to thereby define the filling level in the chamber.