Abstract: A respiratory ventilator and methodology thereof for automatically calibrating respiration gas flow delivery. The ventilator includes a gas flow calibration member having a reader component for recording inspiratory and exhalation gas volume with exhalation time, and for measuring a plurality of incremental exhalation gas flow values in a plurality of incremental time periods during a single exhalation. The gas flow calibration member includes a composite calculator component for determining an average of consecutive composite flow values, and a scanner calculator component for scanning in reverse order the plurality of consecutive composite flow values and calculating a new flow calibration value where a preselected number of consecutive composite flow values fall within a pre-selected flow rate. Thereafter, the gas delivery member is calibrated in accord with the determined new flow calibration value.