All Season Diesel Fuel Additive. Prior to the commencement of each Winter Season, Mobil shall specify the All Season Diesel Additive to be used. As of the Effective Date, Mobil requires the use of the Paramins additive Paraflow 521 stored in Tank 1321. Valero shall be responsible for maintaining, ordering and purchasing, an adequate level of All Season Diesel Additive throughout the Winter Season to meet Mobil's marketing needs. If the additive is not available from the manufacturer, Valero shall immediately notify Mobil in writing. Valero shall not be responsible for additive dosage requirements should the additive not be available. New All Season Diesel Additive receipts must be tested, prior to offloading, for API gravity (ASTM D287/D4052) and appearance (visual clear and bright). The results of such tests should be within the plus or minus 0.5 Deg. API when compared to the certificate of origin provided by the supplier. If the delivered All Season Diesel Additive is off-spec, Valero shall contact Mobil Fuel Technical Support and Paramins personnel. Valero shall invoice Mobil monthly for the All Season Diesel Additive based on usage and the actual price paid for the additive. Payment for such invoices shall be due ten (10) days after receipt. Mobil shall negotiate a price for the All Season Diesel Additive which shall be fixed for the Winter Season. Usage shall be determined by the metered volume of All Season Diesel Additive using specified dosages provided by Mobil. Mobil requires the meters measuring All Season Diesel Additive to be calibrated the month prior to the Winter Season.