Method for determining a vertical position (z_pv) of a horizontally extending interface between a first component and a second component, wherein the first component and the second component are contained in a laboratory sample container in layers that are vertically separated from each other, the method comprising the steps: - generating first data, wherein the first data depend on the vertical position (z_pv) of the horizontally extending interface, - generating second data in form of picture data of the laboratory sample container containing the first component and the second component, - determining a first probability distribution function in response to the first data, wherein the first probability distribution function assigns a probability of the presence of the horizontally extending interface to a vertical position (z), - determining a second probability distribution function in response to the second data, wherein the second probability distribution function assigns a probability of the presence of the horizontally extending interface to a vertical position (z), and - determining the vertical position (z_pv) of the horizontally extending interface depending on the first probability distribution function and on the second probability distribution function, - wherein the first data are generated by sensing a transmittance through the laboratory sample container at different vertical positions (z), and - characterised in that the step of determining the vertical position (z_pv) of the horizontally extending interface depending on the first probability distribution function and on the second probability distribution function is performed by combining the first probability distribution function and the second probability distribution function based on: - Bayes' theorem, and/or - Dempster-Shafer theory, and/or - Kalman filtering. - generating first data, wherein the first data depend on the vertical position (z_pv) of the horizontally extending interface, - generating second data in form of picture data of the laboratory sample container containing the first component and the second component, - determining a first probability distribution function in response to the first data, wherein the first probability distribution function assigns a probability of the presence of the horizontally extending interface to a vertical position (z), - determining a second probability distribution function in response to the second data, wherein the second probability distribution function assigns a probability of the presence of the horizontally extending interface to a vertical position (z), and - determining the vertical position (z_pv) of the horizontally extending interface depending on the first probability distribution function and on the second probability distribution function, - wherein the first data are generated by sensing a transmittance through the laboratory sample container at different vertical positions (z), and - characterised in that the step of determining the vertical position (z_pv) of the horizontally extending interface depending on the first probability distribution function and on the second probability distribution function is performed by combining the first probability distribution function and the second probability distribution function based on: - Bayes' theorem, and/or - Dempster-Shafer theory, and/or - Kalman filtering. - Bayes' theorem, and/or - Dempster-Shafer theory, and/or - Kalman filtering.