Another reason for the performance difference was the re-weighting of features present in the LEF4000 after the addition of tranche 1. Figure visualizes a feature that became more important. Although this feature was present in the LEF4000, the 19 F NMR chemical shift of molecules that contained it in tranche 2 were predicted with a high MAE of greater than 5 ppm after training with only the LEF4000. Less than 1% of the molecules in the LEF4000 contained this bit and even those could be quite different to the ones in tranche 1 and tranche 2. The percentage of molecules that contained this bit in tranche 1 was higher, at around 5%, which made this bit more important by augmenting its relative frequency. Training with the LEF4000 as well as tranche 1 once again improved the MAE of these molecules to around 1 ppm.