The efficiency of energy transferred between two trophic levels is called the TLTE. This stands for 'trophic level transfer efficiency' and is determined by the following formula: TLTE = (production at present trophic level/production at previous trophic level) x100Net production efficiency is used to calculate how efficiently organisms from a trophic level turn the energy they consume into biomass. The formula for NPE is:NPE = (net consumer productivity/assimilation) x100Net production productivity, or NPP, refers to the amount of energy available to organisms on the next trophic level. Assimilation refers to the biomass of the current trophic level after some energy is lost due to incomplete ingestion of food, waste and respiration.