GENERALLY, ALL PRODUCTION ARE CONSIDERED AS PERFECT IN DIFFERENT INVENTORY MODELS. BUT IN REAL LIFE SITUATION IT IS NOT TRUE ALWAYS. IN MY BOOK, I CONSIDER DIFFERENT TYPES OF PRODUCTION OF IMPERFECT QUALITY ITEMS WHICH I HAVE TO CONVERT INTO PERFECT QUALITY ITEMS AND PREPARE FOR SALE. FOR MORE SALE, THE SUPPLIERS ALLOW DIFFERENT DELAY PERIOD OFFERS ON THE PURCHASING COSTS FOR THE RETAILERS. EFFECTS OF INFLATION AND TIME VALUE OF MONEY ARE CONSIDERED FOR MORE ACCURACY IN THE FINANCIAL MATTER.