Art. 56 CISG
If the price is fixed according to the weight of the goods, in case of doubt it is to be determined by the net weight.
The Secretariat Commentary on Art. 52 of the 1978 New York Draft, predecessor to Art. 56 CISG, gives insight into the drafters' unterstanding on the eve of the 1980 Vienna Diplomatic Conference.
Overview of case law on Art. 56 CISG: UNCITRAL Digest
The UNCITRAL Digest on the CISG can be used as a starting point to discover the relevant case law on this article.