an apparatus and method for determining the viscosity of the circulating blood of a living being over plural shear rates caused by a decreasing pressure differential by monitoring the changing weight of the blood , or the changing level of a column of blood over time . the apparatus and method utilize a riser , a capillary tube , a collector and a mass detector , such as a precision balance or a load cell , for monitoring the changing weight of a sample of fluid that flows through these components under the influence of the decreasing pressure differential ; alternatively , the apparatus and method use a column level detector to monitor the changing level of the column of blood over time .