Abstract: Data processing system for calculating the flowrate of air from a pressurized reservoir to an air pressure communication line. A pressure sensor is connected to the reservoir to provide an analog signal indicating pressure, which is converted into a digital pressure signal. The system also has a sensor connected to pressure ports upstream and downstream of an orifice, located between the reservoir and the air pressure communication line. This provides an analog differential pressure signal which is converted into a digital differential pressure signal, which is processed to obtain a first digital flowrate signal. This is combined with the digital pressure signal to obtain a flowrate correction value, from which a revised flowrate value is obtained. This revised flowrate value may be sent to an operator of the system, to a control system, or to an alarm system.