The efficiency of GlyCombo's combinatorial composition assignment algorithm enables computationally expensive features, such as multiple adduct searching and off-by-one error anticipation , which improve the scan annotation rate for mzML files. In Fig 4A, only when sodium is included as an adduct type is the correct (Hex)5 (HexNAc)2 composition assigned to the observed precursor mass. Off-by-one errors not only cause misassignments but also lead to unassigned precursors when the M+1 isotope is mistaken for the monoisotopic peak, even though both produce similar MS2 spectra due to co-isolation for fragmentation (Fig .