Thermal, flow measuring device and method for operating a thermal, flow measuring device. The thermal, flow measuring device has a first sensor with a first heatable resistance thermometer and at least an additional, second sensor with a second heatable resistance thermometer; wherein a decision coefficient is calculated according to the formula DC=(PC1−PC2)/PC1, with PC1(t=t1)=P1,1(t1)/(T1,heated;actual(t=t1)−Tmedium;actual(t=t1)) and PC2(t=t2)=P2,2(t2)/(T2,heated;actual(t=t2)−Tmedium;actual(t=t2)), with P being the heating powers consumed by the corresponding resistance thermometers at the points in time t, and T being the temperature values; wherein the value of the decision coefficient indicates the flow direction of a measured medium in the measuring tube.