A method of determining an electrical capacitance C SW of an electro-mechanical oscillating system comprising a piezoelectric element and at least one further element oscillatingly coupled to the piezoelectric element, the piezoelectric element comprising an electrode and a counter-electrode, comprising the following steps: a) applying an alternating electrical voltage between the electrode and the counter-electrode for the duration of an excitation interval to excite a mechanical vibration of the vibrating system or a subsystem of the vibrating system, such that after the excitation interval has elapsed, the vibrating system or the subsystem performs a free, non-excited vibration, b) after termination of the excitation and during the free, non-excited oscillation of the oscillating system or the subsystem: Measuring a variation over time of a voltage U applied between the electrode and the counter electrode, and c) determining the electrical capacitance C sw, from the variation in time of the voltage U measured in step b), wherein in step b) a measuring device having an internal capacitance C probe and an internal resistance R probe is used to measure the variation in time of the voltage U and wherein step c) comprises the following substeps: aa) determining a variation in time of a DC voltage component U DC from the variation in time of the voltage U measured in step b), bb) determining a characteristic time interval τ, within which an initial value of the DC voltage component U DC, 0 measured in step b) has dropped to the value U DC, 0 le, cc) calculating the electrical capacitance C SW with the characteristic time interval τ. a) applying an alternating electrical voltage between the electrode and the counter-electrode for the duration of an excitation interval to excite a mechanical vibration of the vibrating system or a subsystem of the vibrating system, such that after the excitation interval has elapsed, the vibrating system or the subsystem performs a free, non-excited vibration, b) after termination of the excitation and during the free, non-excited oscillation of the oscillating system or the subsystem: Measuring a variation over time of a voltage U applied between the electrode and the counter electrode, and c) determining the electrical capacitance C sw, from the variation in time of the voltage U measured in step b), wherein in step b) a measuring device having an internal capacitance C probe and an internal resistance R probe is used to measure the variation in time of the voltage U and wherein step c) comprises the following substeps: aa) determining a variation in time of a DC voltage component U DC from the variation in time of the voltage U measured in step b), bb) determining a characteristic time interval τ, within which an initial value of the DC voltage component U DC, 0 measured in step b) has dropped to the value U DC, 0 le, cc) calculating the electrical capacitance C SW with the characteristic time interval τ. wherein in step b) a measuring device having an internal capacitance C probe and an internal resistance R probe is used to measure the variation in time of the voltage U and wherein step c) comprises the following substeps: aa) determining a variation in time of a DC voltage component U DC from the variation in time of the voltage U measured in step b), bb) determining a characteristic time interval τ, within which an initial value of the DC voltage component U DC, 0 measured in step b) has dropped to the value U DC, 0 le, cc) calculating the electrical capacitance C SW with the characteristic time interval τ. aa) determining a variation in time of a DC voltage component U DC from the variation in time of the voltage U measured in step b), bb) determining a characteristic time interval τ, within which an initial value of the DC voltage component U DC, 0 measured in step b) has dropped to the value U DC, 0 le, cc) calculating the electrical capacitance C SW with the characteristic time interval τ.