Mass Flow Controllers add an automated control valve to the mass flow meter to provide gas flows that are proportional to an electronic set point. Although normally used to provide a constant flow rate to reactors operated in a continuous-flow mode, a unique application in batch reactions is to allow the set point to be dictated by the error signal from the reactor pressure transducer. As gas is consumed, the pressure drop signal can be configured to increase inlet flow. This signal can be sent to multiple controllers, enabling the make-up gas to be a mixture with an operator-specified ratio. This technique is often used in the study of co-polymers and ter-polymers.