In a calibration routine, a first set of X-ray recordings of at least one closed first reference package without content is produced, and a mass calibration signature is derived therefrom. A second set of X-ray recordings of at least one closed second reference package having a reference content is produced, and a reference signature is derived therefrom. From the reference signature and the mass calibration signature, a reference measurement value is derived via subtraction. The reference mass of the reference content is ascertained by weighing and assigned to the reference measurement value. In ongoing measurement operation, at least one set of measuring X-ray recordings of closed foil packages each having a content is produced and a measurement signature is derived therefrom. Herefrom, and from the mass calibration signature, measurement values for the individual closed foil packages are derived via subtraction, from which the masses of the contents are quantitatively determined.
