A: Histogram of masses present in the stick spectra in B. In red, marked masses recognised as ubiquitous. B: Stick spectra of five hypothetical peak-lists. Red vertical lines mark the position of ubiquitous masses determined using the histogram in A. C: Single linkage-clustering dendrogram of the peak-lists in B. As dissimilarity the mass measurement range (1500 Da) minus the range enclosed by matching peaks was used. D: Minimum spanning tree.