The service is intended for representative measurements of gases in chimneys using automated measurement systems. The application of the method is limited and applicable to the total measurements of oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen monoxide (NO) and nitrogen dioxide (NO2) or NO and NO2, as well as flue gas temperature. The method is based on the LVS ISO 10396:2007 standard 'Emissions from stationary sources. Sampling for automatic determination of gas emission concentration for permanently installed monitoring systems'. Before making measurements, it is necessary to familiarize yourself with: operating modes of the flue gas source; placement of flues, identifying possible places for connecting measuring devices; flue gas volume flow rates; the expected flue gas composition and the possible presence of interfering substances. It is necessary to ensure that the measured gas concentrations reflect the average conditions in the chimney. The measurement must not be located close to obstacles that could interfere with the gas flow. At the beginning, concentration measurements should be carried out at the cross-section points where measurements are planned to be made, in order to make sure of possible gas stratification or air infiltration.