A measuring apparatus for determining at least one measurand of a measuring medium includes a first measuring device including a first measuring sensor structured to contact the measuring medium and configured to detect measured values of the at least one measurand, the first measuring device embodied to determine a first measured value that is dependent on the at least one measurand of the measuring medium, a sampling device structured to remove a sample from the measuring medium, a second measuring device including a second measuring sensor and embodied to determine a second measured value that is dependent on the least one measurand of the sample, and an electronic control apparatus configured to receive and process the first and second measured value and to perform a verification, calibration and/or adjustment of the first measuring device using the second measured value.