This type of air flow meter was selected out of a large number of potential candidates for having the most promising overall capability. It enables true mass flow measurement. Also, transients and air velocity pulsations can be correctly handled. The most serious draw-back of the hot wire has always been that it is prone to dirt build-up. However, experience accumulated so far, shows that this problem can be avoided by short burn-off intervals triggered a few seconds after the ignition is turned off. The present development has reached a state where the wire can survive a sufficient number of burn-off cycles without changing its properties.