In some examples, a gas mixer comprises a body and an orbital array of gas inlets for receiving one or more constituents of a mixed gas. A mixed gas outlet emits a mixed gas from the body and is disposed at a center of the orbital array of gas inlets. A central gas mixing point, separate from the mixed gas outlet, comprises an internal volume disposed within the body and is surrounded by the orbital array of gas inlet. The internal volume is in fluid communication with the orbital array of gas inlets via a corresponding array of gas pathways extending from the internal volume to each of the gas inlets. Each gas path length of the respective gas pathways is the same. Control circuitry is configured to control gas flow rate within each of the gas pathways individually.