Method for calculating a quality relating to at least one measuring tube (11.1) of a Coriolis measuring device for measuring a density or a mass flow rate of a medium flowing through the measuring tube, where the Coriolis meter has the following: a vibration system with at least one measuring tube (11.1) for guiding the medium, at least one exciter set up to excite measuring tube oscillations and at least two sensors for detecting the measuring tube oscillations, the exciter and/or the sensors each having at least one magnet device with a permanent magnet and a coil device, a carrier body for carrying the at least one measuring tube, an electronic measuring/operating circuit arranged to operate the exciter and arranged to provide measured values of the density and/or the mass flow rate and to carry out the method, an electronics housing in which the electronic measuring/operating circuit is arranged, wherein the method comprises at least the following steps: relating at least one excitation input variable of the at least one exciter to at least one output variable of at least one sensor, the excitation input variable being an excitation force, Determination of an actual vibration characteristic of the vibration system on the basis of a vibration model of the measuring tube and the reference, Determining a standard vibration characteristic of the measuring tube under standard conditions from the current vibration characteristic of the vibration system, wherein the current vibration property is a current modal stiffness, and wherein the standard vibration property is a modal stiffness at standard conditions, characterized in that at least one of the following variables is used in at least one of the process steps: at least an accumulated time over which the magnet system is exposed to a temperature above a respective threshold temperature. a vibration system with at least one measuring tube (11.1) for guiding the medium, at least one exciter set up to excite measuring tube oscillations and at least two sensors for detecting the measuring tube oscillations, the exciter and/or the sensors each having at least one magnet device with a permanent magnet and a coil device, a carrier body for carrying the at least one measuring tube, an electronic measuring/operating circuit arranged to operate the exciter and arranged to provide measured values of the density and/or the mass flow rate and to carry out the method, an electronics housing in which the electronic measuring/operating circuit is arranged, wherein the method comprises at least the following steps: relating at least one excitation input variable of the at least one exciter to at least one output variable of at least one sensor, the excitation input variable being an excitation force, Determination of an actual vibration characteristic of the vibration system on the basis of a vibration model of the measuring tube and the reference, Determining a standard vibration characteristic of the measuring tube under standard conditions from the current vibration characteristic of the vibration system, wherein the current vibration property is a current modal stiffness, and wherein the standard vibration property is a modal stiffness at standard conditions, characterized in that at least one of the following variables is used in at least one of the process steps: at least an accumulated time over which the magnet system is exposed to a temperature above a respective threshold temperature. relating at least one excitation input variable of the at least one exciter to at least one output variable of at least one sensor, the excitation input variable being an excitation force, Determination of an actual vibration characteristic of the vibration system on the basis of a vibration model of the measuring tube and the reference, Determining a standard vibration characteristic of the measuring tube under standard conditions from the current vibration characteristic of the vibration system, wherein the current vibration property is a current modal stiffness, and wherein the standard vibration property is a modal stiffness at standard conditions, characterized in that at least one of the following variables is used in at least one of the process steps: at least an accumulated time over which the magnet system is exposed to a temperature above a respective threshold temperature.