HRS §490:2A-202
Final written agreement: outside evidence
This section says that when a written record is meant to be the final deal, you cannot use earlier agreements or spoken side deals to change it. You can use trade customs or consistent extra terms to explain it, unless the record says it is complete.
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The statute, as written — 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 the terms as are included therein shall not be contradicted by evidence of any prior agreement or of a contemporaneous oral agreement but may be explained or supplemented by: (1) Course of dealing or usage of trade or by course of performance; and (2) 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.
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