Top left: Kiel diagram of the APOGEE DR16 stars (used in the training sample), colour-coded with overall [M/H]. Top right: for the same stars, trained labels, averaged over 80 trained CNN. Bottom left: APOGEE DR16 parameters of the test sample. Bottom right: trained labels, averaged over 80 trained CNN, for the same test sample. Right panels: what the network learns from the APOGEE parameters (left panels).