Bonell, Michael Joachim, The Relevance of Courses of Dealing. Usages and Customs in the Interpretation of International Commercial Contracts, in: UNIDROIT (ed.), New Directions in International Trade Law, 2 Vols., Dobbs Ferry, NY 1977, at 109 et seq.

Nevertheless, on the Basis of a functional and not merely a conceptual comparison of them, it should not be difficult to discover how it has become an almost universally recognised principle that in the construction of ambiguous or incomplete contractual terms, regard must be had, especially between merchants, to the normal meaning of such terms and the usual practices in the respective trade sectors, and this independently of the intention or even the knowledge of the Parties.