The static pressure, the differential pressure, and the temperature must be known in order to be able to determine the mass flow rate, the volumetric flow under standard conditions, or the enthalpy flow of a fluid. Desired variables are detected by individual sensors located in an integrated sensor unit, and the values detected by the individual sensors are then processed in a computing unit that is also integrated in the sensor unit. The sensor unit outputs a value, which also takes other parameters and/or physical constants into account, to a control unit that is connected downstream. Some of the computing is advantageously done in the sensor unit so that some load is relieved from the control unit.