In allometric scaling, maximum potential life span (MPLS) is directly related to metabolic rate (MR), where MR is the recharge rate of a biomass made up of covalent bonds. That biomass (W) is subjected to deterioration over time from thermodynamic, entropic pressure. Metabolism is essentially understood as redox coupling, and has nothing to do with thermogenesis. Metabolic efficiency (ME) is then expressed as the efficiency of this coupling, a ratio of amperes captured and used by biomass, to the amperes available for that purpose. MR is measured in watts, W is measured in grams. These factors are combined in a power law, an elaboration on Kleiber's law relating MR to W and MPLS, that appears as MR = W^ (4ME-1)/4ME. When ME is 100%, MR = W^3/4; this is popularly known as quarter power scaling, a version of allometric scaling that is premised upon unrealistic estimates of biological efficiency.