1. A method for populating a function implemented in a control unit with data, comprising: performing a measurement on a test stand on a system at different measuring points to produce obtained measured values; setting up a global data-based model on the basis of the obtained measured values; performing a virtual measurement that simulates a real measurement on the test stand on the global data-based model, ascertaining an uncertainty for a virtual measured value of the virtual measurement is ascertained from the global data-based model; taking into account the uncertainty of the virtual measured value when populating the function for the control unit with data; detecting on the basis of the uncertainty of the virtual measured value whether a quality of the data-based model is insufficient in at least one range of the measuring points for populating the function with data; if the quality of the data-based model is insufficient in at least the one range of the measuring points, obtaining an improvement of the data-based model on the basis of a supplementary measured value from a supplementary measurement on the test stand; if the quality of the data-based model offers a required quality for populating the function with data, populating the function implemented in the control unit with data in that a measured values from the virtual measurement is entered into a tool, in which an optimization of a label of the function implemented in the control unit is performed; and operating a physical process of an engine by causing the control unit to execute the populated function.