The method for manufacturing a controller (17) comprises providing a combustion system test rig (1), operating the combustion system test rig (1) with different operating parameter sets, measuring the local temperature of the hot gas stream with the at least two temperature sensors (13), obtaining local temperatures-operating parameter sets data, for each operating parameter set calculating, based on the supplied oxidizer and fuel mass flow, a theoretical mixer exit temperature (MET), providing a correlation between the local temperatures and the theoretical mixer exit temperature (MET), programming the controller (17) with the correlation.