The invention relates to a method for ascertaining a physical parameter of a gas using a measuring sensor with at least one measuring tube for conducting the medium, wherein flexural vibrations of different modes with different natural frequencies can be excited in the measuring tube. The method has the following steps: ascertaining the natural frequency of the f1 mode and the f3 mode (110); ascertaining previous density values (120) for the gas being conducted in the measuring tube on the basis of the natural frequencies of the f1 mode and the f3 mode; and ascertaining a value for the speed of sound of the gas conducted in the measuring tube and/or at least one correction term (130) and/or density error, which is dependent on the speed of sound and the natural frequency of a mode, for the previous density value, which has been ascertained on the basis of the natural frequency of the mode, in order to determine a corrected density measurement value (140) and/or a correction term for a previous mass flow rate value in order to determine a corrected mass flow rate measurement value on the basis of the first previous density value, the second previous density value, the natural frequency of the f1 mode, and the natural frequency of the f3 mode.