A seeding and/or fertilizing machine (10) and a method of determining flow in such a machine is presented. The machine comprises a tank (12, 14) of particulate material, a material metering structure (40) and an air delivery system (34) for conveying the material from the tank (12, 14) to the ground. To provide improved metering accuracy it is proposed to include a flow determining device, wherein said flow determining device comprising a first sensor (100) located in the air delivery system (34) for providing a first signal indicative of the force of the particulate material impacting the first sensor (100)； a second sensor (114, 116) located in the air delivery system (34) for providing an interference signal indicative of one or more variables that negatively impact first sensor accuracy； and a processor (90) connected to the first and second sensors (100, 114, 116) for determining a particulate material mass flow signal in dependence on the impact sensor signal and the interference signal.
