ristlõiget läbinud õhu voo koguse suhe selle ristlõike läbimiseks kulunud ajaga, ratio of the quantity of air passing through the cross-section of the flow sensor and the time taken for this quantity to pass through this section, Q = dV/dt, kus V on tegelik õhuvoo maht ja t on aeg, mis kulus selle õhuvoo mahul arvesti läbimiseks, Q = dV/dt, where V is actual volume of air flow and t is time taken for this volume to pass through the meter