Quantifying similarity for spectra with a large number of overlapping transitions: Examples from soft X-ray spectroscopy

•Explores unbiased way to compare spectra with many partially overlapping peaks.•Advances the understanding of similarity measures for automated assessment of continuous spectral properties.•Analyzes the relation between parameters in the similarity measure and the expected simulation errors.•Contributes to understanding of the stability of the multiconfigurational simulations of x-ray spectra.