In this work, we suggest that DFT is subject to proportional error. We show how the standard formation energy correction method, which considers only additive errors, causes unphysical formation energy predictions near the corners of phase diagrams and how that can lead to incorrect conclusions and false discoveries. We propose a one-parameter correction method, which considers proportional error, and show that it does not suffer from the same problems. We also show that it is more robust than the standard correction, and that the 110% PBE method outperforms the standard correction method with respect to matching both experiment and higher level theory: the r2SCAN functional. Overall, we stress the importance of publishing uncorrected results and considering proportional error in all cases where DFT data is fit to experiment. This plot demonstrates the improved robustness of our correction compared to the standard correction with respect to randomly subsampling the training data. 30% of the data was held out for validation, and the remaining 70% of the data was used for training but subsampled randomly 40 times. Each draw selected a random half of the training data. Then, for each draw, both the standard correction method and our method were fit on the training data and used to correct the holdout data. The standard deviation of the predictions on all points in the holdout dataset were calculated, and the one that varied the most is plotted here. In other words, the structure whose corrected formation energy was most sensitive to randomly subsampling the training data is shown here. Specifically, the residual (actual -predicted) formation energy per atom is plotted using correction models fit to each random subset of the training data. The 95% confidence interval is also plotted. and frequent conversations with SKS and JSB. BAR wrote the paper, and JSB, and SKS provided edits and comments.