From the molar flow rates and the measured RTD function, 𝐹 , of the internal standard Ar (see eq. ( )), a theoretical step response, 𝑛̇ , , for each species is calculated (eq. ( )). This represents the response in case that the steady-state kinetics apply for the transient operation, as well, with 𝑛̇ ↑ and 𝑛̇ ↓ as upper and lower reference values, i.e. the molar flow rates directly before each of both switching events.