a payment towards meeting a liability that is not the full amount of the liability. The sum paid will be credited to the account of the payer in the books of the payee as a part-payment of the ultimate liability.
... the successful tenderer may on request receive a payment on account equal to 90 % of the amount obtained by multiplying the net quantities taken over for a product, a destination and a delivery date by the unitary amounts indicated in his tender.
