A system for accurately weighing a mass of material, including a closed chamber (20) having a gas inlet (22) and a gas outlet (24). A scale (30) is disposed in the closed chamber (20). An inert gas supply, under positive pressure, is connected to the gas inlet (22) and a vacuum powered pressure regulator (100) is connected to the gas outlet (24) to maintain a predetermined pressure level within the closed chamber (20) and to substantially inhibit pressure fluctuations within the chamber (20) that may affect accuracy of the scale (30).