Abstract: A mass flow grain monitor is located adjacent the upper end of the clean grain elevator assembly of a harvester and includes a load cell having a member that is subject to slight deformation under loads for use in generating an output signal that is proportional to the load. As the grain flow reaches the top of the elevator assembly, its direction is changed such that a centrifugal force is exerted by the moving flow that is proportional to the mass of the grain flow at that instant. Such centrifugal force is directed vertically against the deformable member of the load cell which is itself generally horizontally disposed when the harvester is on level ground so that the entire weight of the deformable member can be treated as tare and zeroed out of the system when it is calibrated with the harvester on level ground.