A distribution apparatus (10), shown in the form of an agricultural air seeder is disclosed having sensors (110, 112, 114, 116) to measure the mass flow through the distribution system (34), sensors (104) to weigh a tank (12, 14) and a product therein, and sensors (106) to measure the quantity of product in the tank (12, 14). The sensors (104, 106, 110, 112, 114, 116) are used to measure the change in the quantity of product in the tank (12, 14) during a calibration process where the apparatus (10) is operated over an area and the number of rotations of a meter (40) are recorded. The data is then used to determine a mass flow rate per revolution of the meter (40). The method further comprises monitoring in which an area to empty and product needed to complete a field or task is displayed to the operator.
