Uniform Commercial Code

U.C.C. - ARTICLE 2 - SALES
..PART 2. FORM, FORMATION AND READJUSTMENT OF CONTRACT

§ 2-202. Final Written Expression: Parol or Extrinsic Evidence.

Terms with respect to which the confirmatory memoranda of the parties agree or which are otherwise set forth in a writing intended by the parties as a final expression of their agreement with respect to such terms as are included therein may not be contradicted by evidence of any prior agreement or of a contemporaneous oral agreement but may be explained or supplemented

• (a) by course of dealing or usage of trade (Section 1-205) or by course of performance (Section 2-208); and
• (b) by evidence of consistent additional terms unless the court finds the writing to have been intended also as a complete and exclusive statement of the terms of the agreement .