For each predicted amino acid spectrum within each MS library, three measurements of accuracy were calculated (also see NIST-MS 2017 (ii) MoNA f (iii) a hand curated set of amino acids (IOCB). Accuracy for predicted spectra is measured in terms of (A) spectral root mean square error (RMSE), (B) spectral contrast angle (SCA), and (C) weighted cosine similarity (WCS). For SCA, angles below ~26 degrees (shown in green) are typically adequate for library search algorithms . For WCS, the metric used as the training metric within the NEIMS algorithm, scores greater than 0.7 (shown in green) are generally classified as 'similar' .