Left panel: Action space (normalized to the sum of the three actions of motion, Jtot) of Gaia RVS stars with metallicities [Fe/H]<−0.55, along with a zoom-in of the area that we use to select our thin disc sample. The x-axis displays the normalized angular momentum, which is equivalent to the azimuthal action of motion, and the y-axis the normalized difference of vertical action and radial action. Their mean uncertainties are displayed in black in the top right corner. Right panel: Metallicity distribution functions, in logarithmic scale, derived from our thin disc samples of Gaia DR3 RVS, GALAH, and APOGEE stars.