Combining a plurality of local flow measurements made at more than one location to generate a composite flow value can improve the accuracy of the overall measurement. The reliability and long term accuracy of a multi-sensor flow measurement are improved by a two-step process. During an initial learning period, when all of the local sensors are providing accurate local measurements, a calibration table is built up that associates each calculated composite flow value with the set of local flow signal values from which it was calculated. In a subsequent operational period each time the composite flow rate is to be determined the flow meter apparatus first checks to see if all the local sensors are working properly and, if one of them is not working properly, its output is replaced with the corresponding value from the calibration table.