(1) Where the purchase price is calculated according to the weight of the goods, the weight of the packaging (tare weight) is to be deducted, unless otherwise dictated by the contract or the commercial customs prevailing at the place at which the seller is to fulfil the contract.
(2) Whether and to what extent the tare weight is to be deducted at a specific rate or ratio instead of ascertaining it precisely, and whether and how much allowance of extra weight is to be calculated in favour of the buyer or may be demanded as compensation for damaged or unserviceable parts (tret), is determined by the contract or in accordance with the commercial customs prevailing at the place at which the seller is to fulfil the contract.