"[CISG] Article 56 is in the same terms as the corresponding provisions of ULIS." Hager in Commentary on the UN Convention on the International Sale of Goods, Peter Schlechtriem ed. (Oxford 1998) 463 [citations omitted].
CISG Article 56 ULIS Article 58
If the price is fixed according Where the price is fixed
to the weight of the goods, in according to the weight of
case of doubt it is to be the goods, is shall, in case of
determined by the net weight. doubt, be determined by the
net weight.