Pick-one-out test. For each plot, each point represents a different reference set star. For a given point in a plot, the x axis value is the APOGEE-derived label and the y axis value is the label prediction from a Cannon model trained on all other (203) reference set stars. Therefore, for each point in each plot, the applied Cannon model is different than that of every other point. The points are coloured by their model χ² values. The bias and rms of each distribution are given in the top left corner of each plot.