Procedure designed to determine a mass flow of a gaseous medium using a thermal mass flowmeter, wherein said flowmeter has at least a first temperature sensor around which the medium can flow, wherein said flowmeter has at least a second temperature sensor around which the medium can flow, wherein the first temperature sensor is spaced at a distance from the second temperature sensor, wherein the first temperature sensor is heated with a heating power Q, wherein the transfer of heat from the first temperature sensor to the medium depends on the mass flow of the medium, wherein the mass flow of the medium is determined depending on a heating power Q and a temperature difference ΔT m = T 1 - T 2 between the measured values of the first temperature sensor and of the second temperature sensor by means of a power coefficient PC = Q/ΔT, wherein a corrected power coefficient PC corr is determined from corrected values of the temperature difference ΔT in that at least a correction is made using at least a recovery correction term K i, wherein the recovery correction term K i has the form K i = Δ x · u 2 / 2 · c p where u is a value for the flow velocity of the medium, where c p is a value for the thermal capacity of the medium, where Δ x is an element of the group {Δ 1; Δ 2; Δ 12}, where Δ 1:= e 1 -c r, Δ 2:= e 2 -c r et Δ 12:= e 1 -c 2 = Δ 1 - Δ 2, where e 1 and e 2 are the recovery factors of the first and second temperature sensor, and where c r is a constant reference value for which the following applies c r ≤ 1, characterized in that the first and the second temperature sensor have different forms in terms of flow efficiency, and the first and the second temperature sensor have different recovery factors e 1, e 2, wherein the recovery correction term K i should be subtracted from a temperature difference ΔT or added to the temperature difference ΔT to get a corrected temperature difference ΔT corr which is used as a divisor or a factor in determining a corrected power coefficient PC corr. wherein said flowmeter has at least a first temperature sensor around which the medium can flow, wherein said flowmeter has at least a second temperature sensor around which the medium can flow, wherein the first temperature sensor is spaced at a distance from the second temperature sensor, wherein the first temperature sensor is heated with a heating power Q, wherein the transfer of heat from the first temperature sensor to the medium depends on the mass flow of the medium, wherein the mass flow of the medium is determined depending on a heating power Q and a temperature difference ΔT m = T 1 - T 2 between the measured values of the first temperature sensor and of the second temperature sensor by means of a power coefficient PC = Q/ΔT, wherein a corrected power coefficient PC corr is determined from corrected values of the temperature difference ΔT in that at least a correction is made using at least a recovery correction term K i, wherein the recovery correction term K i has the form K i = Δ x · u 2 / 2 · c p where u is a value for the flow velocity of the medium, where c p is a value for the thermal capacity of the medium, where Δ x is an element of the group {Δ 1; Δ 2; Δ 12}, where Δ 1:= e 1 -c r, Δ 2:= e 2 -c r et Δ 12:= e 1 -c 2 = Δ 1 - Δ 2, where e 1 and e 2 are the recovery factors of the first and second temperature sensor, and where c r is a constant reference value for which the following applies c r ≤ 1, characterized in that the first and the second temperature sensor have different forms in terms of flow efficiency, and the first and the second temperature sensor have different recovery factors e 1, e 2, wherein the recovery correction term K i should be subtracted from a temperature difference ΔT or added to the temperature difference ΔT to get a corrected temperature difference ΔT corr which is used as a divisor or a factor in determining a corrected power coefficient PC corr.