When testing the engine for NOx emissions, the reference fuel is Marine Diesel Oil (Distillate) and the test is performed according to ISO 8178 cycles. The NOx value has to be calculated using different weight factors for different loads that have been corrected to ISO 8178 conditions. An Engine International Air Pollution Prevention (EIAPP) certificate is issued for each engine showing that the NOx level complies with the Annex VI to Marpol 73/78.