The term course of dealing is defined in the Uniform Commercial Code as follows: A "course of dealing" is a sequence of conduct concerning previous transactions between the parties to a particular transaction that is fairly to be regarded as establishing a common basis of understanding for interpreting their expressions and other conduct.
"Course of dealing," as defined in subsection (b), is restricted, literally, to a sequence of conduct between the parties previous to the agreement.
An integration clause in a contract, stating that the parties intend the writing to be a complete and exclusive statement of the terms of the agreement does not suffice to negate the importance of course of dealing, "because these are such an integral part of the contract that they are not normally disclaimed by general language in the merger clause.
[3] By contrast, "Under the UCC, the lack of facial ambiguity in the contract language is basically irrelevant to whether extrinsic evidence ought to be considered by the court as an initial matter.
"[4] Evidence of course of dealing will be disallowed, however, if it is "carefully negated" in the parties' contract by "specific and unequivocal" language.