ORS 72.2020: Final 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 record 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:

      (1) By course of performance, course of dealing or usage of trade as provided in ORS 71.3030; and

      (2) By evidence of consistent additional terms unless the court finds the record to have been intended also as a complete and exclusive statement of the terms of the agreement.