Abstract: A monitoring system for computing mass flow of cleaned grain in a harvesting machine such as a combine. The monitoring system includes a system for conveying clean grain from a grain receiving area on the combine and along a predetermined path of travel to a clean grain storage bin on the combine. A grain weighing station is interposed along the predetermined path of grain travel between the grain receiving area and the storage bin. The weighing station is displacable in response to clean grain passing thereover. A measuring apparatus, including a load sensor arranged in combination with and monitoring the displacement of the weighing station, computes the mass flow of clean grain into the storage bin as a function of the displacement of the weighing station.