In a method for calibrating a measuring device, a signal of a first sensor is mapped to a measured value based on a mapping specification. A current measured value of the measuring device is recorded as current calibration measured value; a laboratory reference sample of the measured medium with properties of the calibrated measured value at the point in time of the recording is supplied to a laboratory reference measuring device; the actual value of the measured variable is ascertained based on the laboratory reference sample and made available and recorded as current laboratory reference measured value; and, based on the current calibration measured value, as well as the current laboratory reference measured value, the mapping specification is updated. At least one earlier value pair of a calibration measured value and an associated laboratory reference measured value ascertained in an earlier calibration is considered in updating the mapping specification.