We note that similar ideas were proposed also within the energy domain. In theoretical work of Srnec et al., the sum and difference of the reduction and acidobasic potentials of an isolated reactant were used to define potential duality and disparity. Combining these quantities for donor and acceptor led to a definition for asynchronicity, which describes the concertedness of the PCET process, and for frustration, which describes the similarity of the charge-separated species. Our work offers definitions using quantities researchers might find more intuitive (i.e. PC and ET dimension), directly referenced from the donor-acceptor pair.