One possibility might be that similar to how peptide spectral match (PSM) identification rate can be reported from DDA data, in DIA data it may instead be the average number of peptides identified per DIA MS2 window per retention time window (since each window is deliberately chimeric and can yield multiple peptide matches ). Moreover, as multiple spectra are often used for quantitation in DIA, the number of data points per chromatographic peak is informative on the quality of the quantitative data. For some isobaric labeling methods, generating reporter ions at low m/z, such as iTRAQ or TMT , the resolving power and background in the reporter ion m/z region is particularly important for quantitative accuracy, whereas such measures have little relevance in label-free experiments. Though not discussed here, mass spectrometry-based metabolomics and lipidomics have many similarities in methods and approaches , albeit using different materials. Likewise, spatial methods such as MALDI and DESI mass spectrometry imaging require spatially informative QC samples and metrics , but these deserve special consideration and are outside the scope of this primer. Finally, when working in an unfamiliar tissue or species, QC materials become even more valuable since otherwise poor performance could be chalked up to data being "first of its kind" or due to the fasta used in searching, when in reality it could be underlying methodological or technical issues. Although using a tissue-and species-specific QC2 level material is optimal, this may not be possible, and in these cases some sort of QC material should still be used, regardless. Overall, there are many approaches to implementing QC, but we encourage cores to adopt some QC since any QC is better than no QC.