1. A method for determining a state variable x from at least one sensor value by a cost function prepared for a measurement value y for use in an arithmetic unit of a sensor system having at least one sensor, wherein the cost function depends on the respective state x to be measured and indicates deviation of an actual measured value from a calibration as a function of the state x in order to determine from this minimum the sought state x, the improvement comprising: providing at least one approximation function based on at least one approximation region within the state region x to obtain an approximation of the cost function with approximation functions with negligible error, wherein the sums of the approximation regions cover the entire relevant state region, and determining all local minima on the basis of the approximation, at least in a selection of approximation regions,