After the EM is calculated, the EMD for the monoisotopic and isotopologue mass can be obtained according to equation 2 (i.e., EMD mono and EMD iso , respectively). These EMD values are used to calculate the delta EMD (dEMD) for an mono-iso pair (Equation ). It is important to note that the EMD mono should always be subtracted from the EMD iso and not vice versa when using the probabilistic isotopologue classification model described in this paper. An example case for calculating the dEMD value can be found in figure . The full set of isotopologue and monoisotopic EMD values for the DDS-Tox database can be found on figshare. EM = ion mass × rounded er mass exact er mass (1)