Use of a measuring device for determining the calorific value of a gas flow in a gas line of a gas distribution network , - wherein the measuring device comprises a calorific value sensor which is configured to measure a value for the gas calorific value of a gas in a gas line , and - wherein the measuring device has a control device which is configured to determine a value for the calorific value of the gas flow from the measured value for the gas calorific value and optionally further obtained measured values relating to the gas flow , - wherein the gas distribution network comprises a gas line system of interconnected gas lines , and - wherein the measuring device is arranged and configured to determine the calorific value of a gas flow through one of the gas lines of the gas line system , characterised - in that a decentralised gas feed-in system is connected to a gas line of the gas line system , wherein the measuring device is configured to determine the calorific value of the gas flow fed into the gas line system by the decentralised gas feed-in system , - in that the control device is configured to determine information about the composition of the gas flow, namely about the hydrogen content, from the determined value for the calorific value, and - in that the decentralised gas feed-in system is configured to control the gas feed into the gas line system as a function of the calorific value of the gas flow determined by the measuring device , namely to reduce or stop the gas feed into the gas line system if the hydrogen content determined from the determined value for the calorific value exceeds a predetermined maximum limit. - wherein the measuring device comprises a calorific value sensor which is configured to measure a value for the gas calorific value of a gas in a gas line , and - wherein the measuring device has a control device which is configured to determine a value for the calorific value of the gas flow from the measured value for the gas calorific value and optionally further obtained measured values relating to the gas flow , - wherein the gas distribution network comprises a gas line system of interconnected gas lines , and - wherein the measuring device is arranged and configured to determine the calorific value of a gas flow through one of the gas lines of the gas line system , characterised - in that a decentralised gas feed-in system is connected to a gas line of the gas line system , wherein the measuring device is configured to determine the calorific value of the gas flow fed into the gas line system by the decentralised gas feed-in system , - in that the control device is configured to determine information about the composition of the gas flow, namely about the hydrogen content, from the determined value for the calorific value, and - in that the decentralised gas feed-in system is configured to control the gas feed into the gas line system as a function of the calorific value of the gas flow determined by the measuring device , namely to reduce or stop the gas feed into the gas line system if the hydrogen content determined from the determined value for the calorific value exceeds a predetermined maximum limit. <EOS>