A portable cooler assembly comprises a base and a collapsible container defining a cooler. Some nucleating agents may be used also as clarifiers to reduce the visual haze in finished polymeric articles, thereby increasing clarity of finished polymeric articles. , a xerographic, device use sheet parameters regardless of the tray or bin with which the sheets are associated, separate tallies of sheet registration correction factors for both sides of a sheet, and use registration errors detected on a first side of a sheet to generate correction factors concerning proper registration of the second side of that sheet.