Use of a measuring device (22, 62, 108, 110, 124) for determining the calorific value of a gas flow (31, 67) in a gas line (30, 66, 96) of a gas distribution network (92, 122), - wherein the measuring device comprises a calorific value sensor (34, 68) which is configured to measure a value for the gas calorific value of a gas in a gas line (30, 66, 96), and - wherein the measuring device has a control device (32, 64) which is configured to determine a value for the calorific value of the gas flow (31, 67) from the measured value for the gas calorific value and optionally further obtained measured values relating to the gas flow (31, 67), - wherein the gas distribution network (92, 122) comprises a gas line system of interconnected gas lines (30, 66, 96), and - wherein the measuring device (22, 62, 108, 110, 124) is arranged and configured to determine the calorific value of a gas flow (31, 67) through one of the gas lines (30, 66, 96) of the gas line system, characterised - in that a decentralised gas feed-in system is connected to a gas line (30, 66, 96) of the gas line system, wherein the measuring device (22, 62, 110, 124) is configured to determine the calorific value of the gas flow (31, 67) 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 (22, 62, 110, 124), 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 (34, 68) which is configured to measure a value for the gas calorific value of a gas in a gas line (30, 66, 96), and - wherein the measuring device has a control device (32, 64) which is configured to determine a value for the calorific value of the gas flow (31, 67) from the measured value for the gas calorific value and optionally further obtained measured values relating to the gas flow (31, 67), - wherein the gas distribution network (92, 122) comprises a gas line system of interconnected gas lines (30, 66, 96), and - wherein the measuring device (22, 62, 108, 110, 124) is arranged and configured to determine the calorific value of a gas flow (31, 67) through one of the gas lines (30, 66, 96) of the gas line system, characterised - in that a decentralised gas feed-in system is connected to a gas line (30, 66, 96) of the gas line system, wherein the measuring device (22, 62, 110, 124) is configured to determine the calorific value of the gas flow (31, 67) 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 (22, 62, 110, 124), 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.